Aqua Drive System- A Technical Guide

Japan Fluid Power Association

Copy right © 2001 by Japan Fluid Power Association

Front cover: Copy right © Town of Asakura, Fukuoka Prefecture, Japan.
Triple water mills, a national registered monument
Back cover: Fukuroda-no-taki, Ibaragi Prefecture, Japan.

Table of Contents

1

Overview of Aqua Drive System .................................. p. 1
1.1
1.2

2

3

What is the aqua drive system?............................... P. 1
Advantages and problems to be solved ................... P. 2

Operating Aqua Drive System .................................... P. 11
3.1

Technical issues of ADS .......................................... P. 12
3.1.1 Pressure loss in a pipeline .............................. P. 12
3.1.2 Cavitation and erosion .................................... P. 13
3.1.3 Surge pressure prevention.............................. P. 14
3.1.4 Frequency characteristics with use ................. P. 17
of servovalve

3.2

ADS operational guideline ....................................... P. 18
3.2.1 Water quality evaluation test ........................... P. 18
3.2.2 Control and maintenance of water quality ....... P. 21
3.2.3 System operation temperature........................ P. 21
3.2.4 Effectiveness of cooler .................................... P. 23

3.3

Other issues............................................................. P. 24

Components for Aqua Drive System ........................... P. 3
2.1

2.2

2.3

Components and accessories ................................. P. 3
2.1.1 Pump .............................................................. P. 3
2.1.2 Actuator .......................................................... P. 4
(Water hydraulic motor and cylinder)
2.1.3 Control valve ................................................... P. 5
2.1.4 Pipe and Coupling .......................................... P. 6
2.1.5 Reservoir ........................................................ P. 7
2.1.6 Accessories .................................................... P. 7
(Filter, accumulator and others)
Working fluid ............................................................ P. 9
2.2.1 Working fluid ................................................... P. 9
2.2.2 Water quality ................................................... P. 9
Materials ................................................................ P. 10

4

Application of Aqua Drive System ............................. P. 25

Reference ............................................................................ P. 27
JFPA Water Hydraulics Committee Members ................... P. 27

Chapter 1 Overview of Aqua Drive System
1.1 What is the aqua drive system?
Fluid power technology using water as its pressure medium was already utilized at the end of the 18th century. It was mainly to transmit a large power.
However, the water hydraulic technology at the time had problems, such as low efficiency due to leakage, deterioration of materials due to wear, friction, andrust. All these were blamed on low viscosity of water. Not to mention, nothing was done to treat and maintain the working water.
Later, various kinds of water-based working fluids, of which rust-prevention, corrosion resistance, and lubricating properties having been improved byadding additives to the water, have begun to be used for press and mining machines. The major advantage offered by these water-based working fluids isflame resistance; therefore, they have been well applied to iron manufacture facilities where the danger of fire was the most concern. A water hydraulicdrive system today is often recognized just as "water hydraulics" in a broader sense, which generally includes water-based working fluids.
The “aqua drive system (ADS)”, different from the water hydraulic driving technology describedabove, solely uses tap water or pure water for its system working fluid.

Change of Market

Aqua Drive
Technology
COST

Oil-freeOverall Evaluation by LCA

Progress of Technology

Fig. 1.1 Three elements supporting
aqua
drive
technology

1

The basic policy is “oil-free”.
 The aqua drive system is consisted of components without lubricating oil, working oil, andmechanical oil.
 The driving characteristics of the aqua drive system are equivalent to those of theconventional driving technologies, such as by electricity, oil hydraulics and pneumatics.
(2) Life Cycle Assessment (LCA), is the core concept to evaluate the viability of the system.
 Resource and energy saving
 Environmental conservation, cleanness required for the environmentally sustainable
manufacturing processes, safety in hygiene.
 Overall cost performance including, not only the initial cost but also service, maintenanceand management, etc.
(3) Backup by “high technology”
 Today’s cutting-edge fundamental technologies in the field of ceramics, engineering plastics,
and the advanced surface treatment technology.
 Computer-related technologies, such as in design and analysis, as well as in control, andmanagement.
(1)

Environment
Safety ・ Sanitation
Resource & Energy
Saving1.2 Advantages and problems to be solved(6)
Advantages
(1)
(2)
(3)
(4)

(5)

Availability: the readily available tap water is the working fluid.
Easy to dispose: The used water can be damped to the rivers andsewage without special wastewater process otherwise required.
Low management cost: Costs for purchase and management of thefluid are low.
Low environmental impact: Even upon an accidental leakage
during the operation, the fluid is non-odorous, non-toxic, andharmless.
Superior compatibility with products: The system is very clean
and hygiene control is easy.

(7)

(8)

Fire resistance: The system is safer to the fire. Also, in case offire around the system, it can stand to prevent the fire fromspreading. For this reason, the system is excluded from theapplicable range of the Fire Defense Law. In other words, thesystem is superior to any other driving systems in regards to fire
insurance and safety management.
Low pressure loss: The water’s low viscosity contributes to thepipe pressure loss reduction and to easy system expansion.
Because of this, the user can even save power required whencompared to that required for the oil hydraulic system of the same
size.
Faster response: High fluid stiffness provides faster powertransmission.

Problems to be solved
(1)

(2)
(3)
(4)

Lubrication property, sealing characteristic: Water’s low viscosity
deteriorates the lubrication property. Decreased efficiency byleakage from slight gaps of the system components. Decreased
efficiency by increase of wear and friction on the mating faces ofmoving parts. Deteriorated sealing.
Cavitation prevention: The high-saturated vapor pressure easily
initiates cavitation and erosion, which cause material deterioration.
Rust-prevention: Rust is easy to form.
Water quality maintenance: In the working fluid, bacteria, sludge,
and slime are developed. Metal compounds are deposited.

These problems unique to the “aqua drive system” can be solved throughcareful selection of component structure, materials and by the use ofadvanced designing methods with computer. Applying today’s high-end
technology is also beneficial for the materials and the surface treatment.

2Chapter 2 Components for Aqua Drive System
2.1.1 Pump

2.1 Components and accessories
Pumps

Positive
Displacement
Centrifugal

Actuators

MotorsCylinders

Aqua
Drive
SystemRotaryValves

Axial
RadialVane
Reciprocal
Axial
RadialVane
TurbineDirectional
Pressure
Flow
Servo & Proportional

Piping, Hosing, Fitting
Tanks
Accessories

Controllers

Filters
Accumulators
Heat exchangers
Water quality control units
Sensors
OthersFig. 2.1 Configuring devices and accessories of ADS

3Structure: A water hydraulic pump used for the aqua drive system isselected either from the positive displacement or the centrifugal, according
to specifications and the use of the system. For a time being, a majority ofthe pumps are the positive displacement in the ADS. The centrifugal pump,which has been used widely for the fluid transportation in many industrial
fields, can be used for a low-pressure drive system, due to its low-pressurelevel compared to that of the positive displacement pump.
Displacement: The pump size should be selected such that the required
flow rate and rotational speed are obtained. The flow velocity of theinlet/outlet
is preferred to be within the recommended flow velocity range of the pipe
size.
Rotational speed: The rotational speed should be selected based on thefollowing suction requirements.
 Relative location of the pump and the water surface
 Pressure of the suction port part (upper and lower limits)
 Suction pipe size and length as well as suction filter resistance, etc.
 Necessity of the boost pump
 Installation method

2.1.2 Actuator
Motor

Cylinder

Structure: The positive displacement and turbine types are mainly used.
As the positive displacement motor, the axial piston and the radial piston
motors are commercially available. The vane motor is also available forthe low-pressure use.

Structure: Two cylinder types, the single acting and the double acting, areoffered based on their motion. The user can choose the cylinder from awide variety, such as the plunger, the single and double rods and telescopetypes. However, about the material and the seal system, clearly define thecylinder speed, frequency of operation and loading requirements.

Rotational speed: When the water hydraulic motor is used at a low
rotational speed, the user should select a motor of which rotational speed is
not lower than the value recommended by the manufacturer. If noappropriate motor is available, combine the motor with a reduction gear.
Actuator, integrating a water lubricated type reduction gear and a water
hydraulic motor, is also developed and commercially available; therefore,
the user has a variety of choices according to the use.

Water hydraulic cylinders
Cylinder speed: The user can refer to the recommended speed range ofthe oil hydraulic cylinder for selecting the water hydraulic cylinder speed.
The cylinder should be equipped with a seal system of which sliding
resistance is minimum as possible.
Water hydraulic vane motor

Air vent: The air vent must be installed such that it can automatically ventthe air; otherwise, accessible by human to vent it manually.

4

Chapter 2 Components for Aqua Drive System
Buckling strength: To prevent the cylinder piston rod from being bent or
buckled no matter where it is installed, the user needs to pay attention to
the stroke length, the loading direction, and installation method of thecylinder.
Loading method and excessive load: When the cylinder is used where
excessive or external load can be built up, the user needs to install thecylinder by a method, which takes the expected maximum load or thepressure peak into account.
Pressure amplification: The system must be equipped with a measure sothat the rated pressure does not go beyond the limit because of thedifference of piston areas.

Structure: Two valve types, spool and poppet, are available. The valves
with various functions are commercially available. The inner passage ofthe valve main body and the manifold should have a structure such that theworking fluid does not stay still. The structure prevents the water qualitychange and accumulation of foreign substances caused by the residing
working fluid.
Electric connection of the electric operational valve: The valve has tosatisfy the IEC standard in regards to water- and damp-proof aspects.
Water and moisture proofing of the solenoid part: The user should
select a safe valve according to IEC529 such that ingress of water and dust
from the outside is prevented and leakage of the working fluid from thevalve to the solenoid is prevented.

2.1.3 Control valve
Overview: The water hydraulic valve is classified per functions to control
the pressure, flow rate, and direction of the working fluid. The user canselect various valves tosatisfy the requirements due
to
the
ADS
circuitconfiguration. Spool typeis available for the servo
and proportional valves.
Size: When the valve isused at the maximum flow
rate, the flow velocity in thepipe, which is separately
specified, should be within
the recommended range.

Water hydraulic servovalves

5

Water hydraulic relief valves2.1.4 Pipe and Coupling
Pipe size: Select a pipe size such that the flow velocities in the respective
pipeline should meet the following recommended values:
High-pressure line:
3～8 m/s
Return line:
2～5 m/s
Suction line:
0.5～1 m/s
Note) Comparison of the water and oil hydraulics: The pipe friction loss andsurge pressure due to differences of the water and oil properties have been
calculated on an assumption that the friction and oil flow through the sameline at the same flow rate. The friction loss of the water is generally a halfof that of the oil hydraulics. The surge pressure of the water is generally
1.3 times greater than that of the oil due to water hammer. If the friction
loss value of the water hydraulics is allowed to be equal to that of the oil,the viscosity of the water can be increased up to twice as much as the oil.
However, considering influence of the surge pressure, it is reasonable forthe flow viscosity of the water to be 1.5 to 1.6 times of the oil. Therefore, if
the upper limit of the flow viscosity through the oil hydraulic pipe is assumed
5 to 6 m/s, that of the water shall be 8 to 10 m/s.
Pipe for the high-pressure line: Despite of the velocity being within or
beyond the recommended range described above, the user should consider
possible generation of the surge pressure, depending on the operation
methods and avoid any system damage when selecting the high-pressureline.
Hose assembly: Select a hose assembly confirmed its adaptability with theworking fluid, such as metal jigs and rubber hoses.
Pipe connection: Pipes must have such a shape to allow no outer leakage.
It is not desirable to use any connection method that requires taper screw
threads for pipes or sealer.

Pipeline
Couplings for pipes and hoses: The coupling should be made of theelastic seal. Select the elastic seal confirmed its conformity with theworking fluid.
Rated pressure of coupling: Select the coupling of which rated pressure isbeyond the maximum operational pressure of the system.
Standard of pipe: It is desirable that the selected pipe shall conform tospecifications described in JIS G 3448 (Light gauge stainless steel tubes forordinary piping).

6

Chapter 2 Components for Aqua Drive System
2.1.5 Reservoir
Capacity: The reservoir should be capable of holding the working fluid
circulating in the system as well as be able to maintain a certain water levelof the working fluid that guarantees safe use of the fluid. Also, the user
should select a reservoir while taking water temperature rise, characteristics
of separation of the entrained air and the falling speed of contaminants into
consideration.
Water level: The reservoir should be designed so that a water level of theworking fluid is higher than the pump suction port. Depending on thepump suction requirements, use of pressurizing reservoir or boost pump ispreferred.
Interior surface structure: It is influential to the pump suction requirements.
The circulating speed of the working fluid should allow the sufficient air
discharge to the reservoir. Therefore, separate the suction and returnsides of the pump with a buffer plate or other medium.
Shading: To prevent bacteria and germs growth, the structure should bedesigned so that no direct sunlight enters into the reservoir.
Suction line and its position: The user should use the suction line ofwhich size can obtain the suction characteristics recommended by thepump manufacturer and install it where the line can obtain suchcharacteristics. When a filter for the suction line is to be installed, cleaningor replacement of the filter should be taking into account.
Preventing residual contaminants: Contamination residue and deposit in
the reservoir will cause rusts and help bacteria growth. Therefore, thereservoir structure should be designed such that no contaminants ordeposits could stay on the bottom and at corners of the reservoir, and theworking fluid should be completely drained.

7

Interior surface finishing: It should be finished such that contaminants,
such as sludge, waste lint, scale and others, can be easily removed whenentered.
2.1.6 Accessories
Filter
Filtration: Filtration is required to restrict the particle contaminants below an
acceptable level following operational requirements such as the pressure
range employed for the ADS. Indication of the contamination level should
conform to ISO4406.
Selection: Generally, the inner clearance of the water hydrauliccomponents is narrower than in the oil hydraulics. To select the filter, theuser has to follow standards recommended by the manufacturer. Note thatthe pressure drop when the working fluid is passing through the filter muststay within the specified range provided by the supplier.
Water supply: When the water is supplied for the initial stage or for
maintaining the water level, the user should fill the reservoir with theworking fluid via the filter designed exclusively for water supply. It shouldhave the equivalent or superior filtration accuracy compared to other filters
already supplied to the system.
Pump suction line: The user should select a filter, which matches the
suction requirements provided by the pump manufacturer and build theconfiguration with considerations over maintainability, such as replacementof elements. Note that the user must know some pump manufacturers do
not allow filter installation to the suction line. The user should follow the
instructions provided by the manufacturer and adopt the filtration
configuration suitable for the system.

Accumulator

Others

Structure: Accumulators such as the diaphragm, the bladder and the piston
types are available. The bladder type accumulator is the most popular.
When the water-hydraulics-specified accumulator is specified, the user caneasily select standardized products from commercially available lines.
Such an accumulator can be substituted from the counterpart of the oil
hydraulics in the aspects of function and performance.

Heat exchanger: When the working fluid temperature exceeds the specified(refer to Section 3.2.3, System operation temperature) during natural cool
down, the heat exchanger complying with the working fluid should be used.
To prevent freezing, a heater may be used as required.

Pulsation prevention: If the triple-plunger pump is to be used as the water
hydraulic pump, it is preferred to use the pulsation-absorbing accumulator
according to the required pressure specification of the system.

Air breather: Even when the reservoir is an open type, considering theambient environmental conditions where the pump is installed, the air
breather must be installed to purify the air entering the water reservoir. For
the filtering accuracy, the user should also take the bacteria and germs
flowing in the air into account.
Water treatment unit: Integrating the unit for sterilization, such as
dechlorination, ozonation, ultraviolet treatment, and such into the water
hydraulic unit or pipes as required, can prevent growth of bacteria andgerms.
Various and effective units are commercially available forrespective purpose of sterilization. The user can select the suitable withappropriate specification, which complies with the required water quality andoperations.
Sensor: For safe operation of the system and protection of the water
hydraulic components, equipping the unit with switches such as thepressure switch, the level switch, the temperature switch etc., is desirable.

8Chapter 2 Components for Aqua Drive System
2.2 Working fluid
2.2.1 Working fluid

2.2.2 Water quality

Definition
The “tap water” defined in the Article 69, Ministry of Health and Welfare
Ordinance (1992) (see Table 2.1), shall be the standard working fluid used
for the system.
If the ADS is to be used out side of Japan, serious consideration over thewater quality is required for the tap water standard is assumed different.

Water quality that may seriously affect on the ADS performancepH-value, conductivity, free acid, free carbonic acid
Corrosion:(CO2), chloride ion (Cl-), Cl2, dissolved oxygen,hydrogen sulfide, etc.
Generation of scale: hardness, silica (SiO2), Ca, Mg, sulfuric acid ion(SO42-), oil and grease, etc.
Generation of slime: micro-organism including bacteria

Table 2.1 Standard of the water quality of tap water

Table 2.2 Characteristics of tap water

Item

Test
item
*1

Concentrationof hydrogen ion

pH

5.8 ～ 8.6○

Hardnessmg/  (Ca, Mg etc.)

300 or less○

Chloric ion

mg/ 

200 or less

○

Zinc

mg/ 

1.0 or less

Iron

mg/ 

0.3 or lessCoppermg/ 

1.0 or less

Sodiummg/ 200 or lessManganesemg/ 

0.05 or less

Residue of transpiration

mg/ 

500 or less

Turbidity

Degree2 or loss

General bacteria

Count/m 

100 or less

*1 Refer to Section 3.2.1.

9“tap water” inArticle 69○○

Tap water（20℃）

Item (Unit)(Reference)
Working oil forthe oilhydraulics

Main characteristics of the ADS
Impact of cavitation erosion isheavy.
Friction loss of pipes is small.
(The pipe size can be reduced
more.)The leakage from the clearance issmall.

Density

kg/m3

1000

860 ～ 920

Kinematic
viscositym2/s

1×10-6…(low)Low toenormously
highChange ofviscosity
against thetemperature

―

Small

Large

Bulk
modulusGPa

2.4

1.36 ～ 1.88

kPa

2.34

9×10-6

J/kgK
W/m・
K
℃

4180

2018

The system stiffness is large.
The surge pressure is great andthe damping is slow.
Impact of cavitation erosion isheavy.
Slow temperature rise

0.6

0.13

High cooling effect

Incombustibility

200 ～ 230

No risk of the fire

Vapor
pressure
Specific heat
Conductivity
Flash point

Even if the temperature of thefluid is changed, performance is
not largely changed.

2.3 Materials
Element
Material selection: To select the materials such as corrosion resistantalloys (titanium, aluminum, copper and nickel alloys as well as stainlesssteel, etc.), plastics, ceramics etc., the user should understand and aware of
their mechanical properties, corrosion resistance, workability, thermal
properties, etc.
Surface treatment: The user should choose appropriate method of surface
treatment such as plating, vapor deposition, spraying, etc. according tomaterials, either base or article, and where the item is to be used.
Cavitation erosion: The components should be designed and installed
such that no cavitation occurs. It is desirable to select the materials thatprevent serious damages even when cavitation occurs. The following
materials are superior for strength and workability: Stainless steel,aluminum bronze, nickel aluminum bronze.
Seal for the ADS: The following seal materials are generally known forconformity with water as media in the ADS.
(1)
(2)
(3)

Elastomer: NBR, HNBR, FKM (FPM), etc.
Thermo plastic elastomer: Polyurethane, etc.
Plastic: Filler-containing PTFE, super high-molecular PE, etc.

Pump & Motor

Valve
CylinderMaterial
Ceramics & its Coating,
Stainless Steel,
Titanium Alloy,
Engineering Plastics
Ceramics,
Stainless SteelStainless Steel,
Ceramics & its Coating

Tank

Stainless Steel & Plastics

Filter

Stainless Steel & Plastics

Pipe & Fitting

Stainless Steel & Plastics

Manifold

Notes

Corrosion
Wear
Errosion
Cavitation

Stainless Steel
Table 2.3 Components and materials

10Chapter 3 Operating Aqua Drive System
Currently, the user can easily configure the ADS of capability up to 14 MPa(140 bar) using parts and devices commercially available. However,attention should be paid to some points of the water property and the water
quality.
Low viscosity: The pressure loss of the pipe is smaller than that of the oil
hydraulics. It contributes to designing a smaller system. However,lubricating property is inferior; therefore, when the user use a high pressure,examination of the lifetime is required.
Cavitation: Cavitation is a phenomenon that air bubbles are generated due
to local pressure drop of flowing fluid. Taking some preventive measures isrequired. Selecting materials that can resist to cavitation erosion isimportant. Also, creating the shape of flow effective to prevent thecavitation erosion is important.
Bulk modulus (Fast propagation): Sudden shutdown of the circuit
increases the surge pressure, which indicates the impact is also great.
Consider some methods to prevent the sudden shutdown of the circuit
during operation.
Water quality: To make the tap water as the working fluid, use a reservoir
that prohibits ingression of dusts and foreign materials. Also, shutting off
the direct sunlight is important to prohibit growth of bacteria and microbialorganic materials.
Large specific heat: The rate of temperature rise of water is slower thanthat of the oil when their volumes are the same. With use of a cooler, theexchanged amount of heat is greater than that of the oil, comparing thesame passing flow rate.

11

This chapter summarizes the theoretical and experimental aspects
concerning the items mentioned earlier and divides them into “technologicalconsiderations” to the ADS operation and “operational guideline”.
Particularly, methods to demonstrate the ADS advantages and theeffective ADS operation are focused. The segmented operation of the
input signals with the servovalve proves the possibility to reduce the surge
pressure effectively.
The test result of the frequency response
characteristics with the servovalve used is also shown.
The water quality was monitored for 12.5 months in total using the test
circuit. No phenomenon to induce any trouble was observed.
An example of ADS

hydraulics whereas a subscript o means oil hydraulics.

3.1 Technical issues of ADS

pw w  w
 6.46(Q / d ) 3 / 4po o  o3.1.1 Pressure loss in a pipeline
Water is a fluid of low viscosity and its pressure loss in lines is much lesscompared to that of oil. Therefore, following can be some of the advantages
that water can provide as a working fluid.

dp +Δ pp

 Inner diameter of fluid lines can besmaller.

V

Pressure losses, pw in the water hydraulic pipe line and po in the oil
hydraulic pipeline, are both plotted in Fig. 3.2. See Table. 2.2.
Requirements:
Density  (kg/m3):  w = 1000,  o = 880

Kinematic viscosity  (m2/s):  w = 1.0×10－6,  o = 34.0×10－6

 Energy loss is minimized evenL1when the actuator and pumpshould be separately installed.

1/8 1/4 3/8
1/2 3/4 1

1 1/4

1 1/2

2

2 1/2

Water pressure loss and oil pressure loss, of which flow rates are the sameand are flown in a pipe of the same size, are compared. When a fluid ofdensity  , kinematic viscosity  and flow velocity V is flown in a pipe, of
which inner diameter is ｄ and length is L , the pressure loss p can be
expressed by the following equation.

p 

 L

pw /poFig. 3.1 Pipe

0.5

Turbulent

2V
2d
The coefficientλis the pipe friction coefficient and can be expressed as follows:
0.316464

(laminar flow) and   4(turbulent flow), respectively.
Re
Re
The Reynolds number Re is expressed by the equation Re  Vd / .

Pipes: Schedule 80
0
0

50

100

150

200

250

QQ((L/min)/ min)
Fig. 3.2 Comparison of pressure loss in water hydraulic pipeline
and in oil hydraulic pipeline

Assuming that flow in the water hydraulic pipe is turbulent and the flow in theoil hydraulic pipe is laminar, the ratio of the respective pressure loss can be
expressed by the equation below. In the equation, a subscript w means water

12

Chapter 3 Operating Aqua Drive System
The y-axis indicates the ratio pw / po , while the x-axis indicates flow rate
Q . The pipe size d is taken as its parameter. The pressure loss ratio in
both fluids is smaller than 1 in the range shown in the figure. The pressure
loss ratio obtained in turbulent flows in both fluid types is indicated with abroken line. Also, the ratio remains smaller than 1. From this result, thepressure loss in a water hydraulic pipeline is smaller than that in an oil
hydraulic pipeline.
Due to low kinematic viscosity of water, the pressure loss in a water
hydraulic pipeline is small, and thus, advantageous as a power transmitting
line. Application of water hydraulics to a drive system where the pump andthe control valve or the actuator are separately installed and a compact
system of which pipelines are of small diameter is suitable.
3.1.2 Cavitation and erosion



Cavitation
Cavitation is a phenomenon that local pressure of flowing fluid drops
locally and generates air bubbles (vapor nuclei). The vapor pressure canbe practically regarded as the critical pressure point where the air bubbles
are generated.
The simplest preventive measure is controlling thepressure. For a pump, set system’s operation parameters such as watersupply pipe diameter, length and water such that the lowest pressure in thepump suction area must be exceeding the vapor pressure.
At throttles such as valves, the cavitation coefficient k  ( p 2  pv ) /( p1  p 2 )Cavitation erosion
Cavitation erosion is a phenomenon that component materials aredamaged due to impact pressure generated upon bursting of air bubbles.
To suppress erosion and accompanying pressure fluctuation and noise, it iseffective to reduce the number of bubbles as well as bubble size, toseparate the bubble bursting area away from the material surfaces and toselect anti-corrosive materials for the components.

Critical pressure point of cavitation generation at the throttle anderosion mass
Cavitation is easily occurred by jet fluid at the throttle and valve area
where transiently configured upon switching pressure of a valve or a pump
motor. It is a serious problem to produce much high-pressure machines aswell as to improve their performance and lifetime. Critical point of thecavitation generation caused by the jet can be sorted out with the cavitation
coefficient k and the Reynolds number Re as shown in Fig. 3.3.
The difference of erosion mass is large between by water and by oil. The
erosion mass, which the cavitation water jet was impacted on the test
specimens, was reported 5 to 6 times greater than that by oil.

1: Oil hydraulic fluid A
2: Water-glycol
3: Oil hydraulic fluid B
4: Spindle oil
5: Polymer solution
6: Emulation A, B
7: Surfactant solution
8: Tap water

can be regarded as a threshold, where p1 is an inlet pressure, p 2 is theoutlet pressure and p v is the inlet vapor pressure.
For thecountermeasure, make the figure p 2 high to make k larger than thecritical point by using two-stage throttling and applying backpressure.
Fig 3.3

13

Working fluid types and Re - k characteristics

3.1.3 Surge pressure prevention
Surge Pressure
Generation of surge pressure must be paid attention to when flow rate of a fluid power system is high while demanding sudden run and stop of the system.
In the ADS, the surge pressure becomes higher compared to that of the oil hydraulic system due to properties of water. Therefore, if the user’s ADS is
expected to run for fast action while anticipating generation of excessive surge pressure, excogitating the water hydraulic circuit and devices configuring thesystem in designing stage is desirable. For example, realizing a shock-less drive using some controllable devices, such as a proportional valve and a
servovalve, can be considered.

⊿pWhen the surge pressure is generated by sudden change of valve state due tooperation, the pressure propagates through the pipe, affecting operations of otherdevices. The surge pressure p has a close relationship with the wave propagation
velocity c .

p  cV

－⊿p

V

V－⊿V

Fig. 3.4 Surge pressure generation due to shutting a valve

Propagation velocity: The speed is determined by the bulk modules K and the density
 . It is expressed as c  K ρ . Accordingly, the surge pressure p will be as
shown below, respectively. It can be seen that the water’s surge pressure to the same
flow rate fluctuation V is higher than that of the oil.
Waterp  1.55V (MPa)Note that c  1550 m/s .

Oilp  1.15V (MPa)Note that c  1305 m/s .

Density  (kg/m3) herein is defined as 1000 for water and 880 for oil, respectively.
Kinematic viscosity V (m2/s) herein is defined as 1.0×10－6 for water and 34.0×10－6
for oil, respectively. Bulk modulus K （GPa） herein is defined as 2.4 for water and 1.5
for oil, respectively (see Table 2.2).

14

Chapter 3 Operating Aqua Drive System

15

Surge pressure test in a cylinder drive circuit

port B is connected to the return port. The cylinder and a servovalve areconnected with a 1/4-inch stainless pipe of 30 m long. While the load isdriven at a constant speed, the servovalve is shut suddenly. The valve
was linearly closed. The surge pressure p was measured from thetransient pressure wave of the port B.

Load 50kg

The relationship between the valve shutting time T (s) and the surge
pressure p is described in Fig. 3.6. Circles in the figure indicate themeasured values, and a broken line indicates the result of simulation.
Thus, the result that calculated the pipe dynamic properties by thecharacteristic method and the equation of motion of the servovalve and theload mass was taken into consideration.

Pipe：30m
1/4’

pv2 (MPa)

10

p

The figure shows that the longer the valve shutting time T , the smaller thesurge pressure p becomes.
0

t

0

T

1

6

t (s)

u

A

B

P

T

ps=7MPa
Fig. 3.5 Surge pressure test

Simulated resultsp (MPa)u

4

Experimental results

2
0

0.05

0.1

T (s)
Using a cylinder drive circuit described in Fig. 3.5, an experiment was
conducted to examine the surge pressure that occurs upon a sudden
shutting of a valve. A mass of 50 kg was driven by the double rod cylinder.
Prior to the experiment, the supply port P is connected to the port A. The

Fig. 3.6 Valve shutting time and surge pressure

16Chapter 3 Operating Aqua Drive System
Surge pressure prevention by two-slope valve shutting manipulation

Fig. 3.8 shows the measuring result of the surge pressure T to the valve
throttling time T .

Instead of sudden throttling of the valve, two-slope manipulation caneffectively control the surge pressure.
6

u (V)

Simulated results of a pattern A

p (MPa)In Fig. 3.7, the pattern A shows sudden throttling of the one-stage
manipulation and the pattern B and C show that of the two-slope
manipulation. The test settings were as follows: the valve-opening angleof the breaking point is a constant value (1 Volt). The time of the breaking
point is set to T / 2 , which is the half of the valve throttling time T , or
(3 / 4)T .

4
Experimental results
○: A
□: B
△: C

9 (V)

2
0

Pattern
C
B
A
t (s)

Fig. 3.8 Control of the surge pressure with the two-slope manipulation

T/2(3/4)T
T

Fig. 3.7 Two-slope manipulation

17

0.1

T (s)

1 (V)
0

0.05

The results shows that the surge pressure generated in the patterns B andC, which is the two-slope manipulation is smaller than the pattern A, whichis the one-phase manipulation even when the valve throttling time is thesame. Moreover, the surge pressure in C is smaller than that in B. Thatis because the throttling rate just before the valve is throttled in the pattern
C is slower than that of B.

3.1.4 Frequency characteristics with use of servovalve

1

10

-5

ゲイン(dB)Gain(1) Effect of the water temperature change (10℃ and 45℃)
From the experimental results, we can see that the frequency characteristics
at the subjected temperature did not change for the water viscosity bytemperature change hardly changed.
Circuit: Fig. 3.5, Pipe length: 0.8 m, Cylinder: single rod
Result: Fig. 3.9, Input signal amplitude: constant, Gain: the reference
output (cylinder displacement) amplitude at 0.05 Hz.

Frequency
周波数 (Hz)0-10

L=2m, Ps=7MPa
L=2ｍ, Ps=14MPa
L=32m､ Ps=7MPa
L=32m, Ps=14MPa

-15
-20
-25
-30

Frequency (Hz)

0.01
0

0.1

1

10

Phase
(degree)
位相（°）-5Gain(dB)

-10
-15
-20

10℃
45℃

-25

Frequency
周波数 (Hz)

10

-120
-150
-180

L=2m, Ps=７MPa
L=2m､Ps=14MPa
L=32m, Ps=7MPa
L=32m, Ps=14MPa

-210

-30

-240
Frequency (Hz)

0.01
-90

0.1

1

10

-120

Phase (degree)

1
-90

10℃
45℃

-150

-180

Fig 3.10 Frequency responses (Influence of pipe length)(2) Influence of the pipe length (2 m and 32 m)
Regardless of the water supply pressure, the longer the pipe is, the lower thegain becomes when the input frequency is high. Thus, the phase delay
becomes large. This is considered due to increased pipe friction and decreaseof load pressure at the cylinder.
Circuit: Fig. 3.5, Pipe length: 2 m and 32 m, Supply pressure: 7 MPa
and 14 MPa
Result: Fig. 3.10,
Gain: 14 MPa,
the reference output (cylinder
displacement) amplitude for the pipe length of 2 m.

Fig 3.9 Frequency responses (Influence of temperature change)

18

Chapter 3 Operating Aqua Drive System

19

3.2 ADS operational guideline
3.2.1 Water quality evaluation test
The change of water quality of the tap water during the ADS operation was tracked and tested twice. In the first run, the water temperature was set to
30 ℃ and the run time was 1600 hours (9 months). In the second run, the temperature was set to 40 ℃ and the run time was 1650 hours (12.5 months).
The results of both tests show that no problem was observed in the water quality. In addition, no considerable impact to the water hydraulic components
was also observed.
(1) Test apparatus and conditions
Fig. 3.11 is a view of the water quality test unit. Fig 3.12 is thecircuit diagram of the test apparatus. Before starting the test,
flushing of the apparatus was sufficiently performed. During thetest, the water was circulated without newly supplying any water.
The water used was tap water supplied around the Tokyo
metropolitan area.

14MPa
ON/OFF valve

Ｍ

Plunger pump
21  / min

Sealed reservoir: 100 
Water temp.: 30℃/40℃
Place of installation:
No direct light mustreach to the reservoir.

Fig. 3.11 Water quality test unit

Fig. 3.12 Circuit diagram of the test apparatus

20Chapter 3 Operating Aqua Drive System(2) Inspected items and Test result(3) Analysis and evaluation【Monitored points】

About the pH value, chloride ion, hardness, and residue oftranspiration: While the changes of the water quality were monitored, thevalues of these items remained sufficiently lower than the standard values
for tap water. No great change was observed. No difference was also
observed according to the monitored places.

【Test result】

Fig. 3.13 Apparatus circuit pressure (Experimental value)

About the general bacteria: Excepting the 4th sampling, the growth wasobserved in the initial period (0 to 15 days, up to 120 hours) regardless ofsampling locations. However the number of bacteria then decreases due
to malnutrition and firing.

GeneralBacteria (count/ml)
一般細菌(個/ml)【Monitored items】

Inside of the reservoir, just before the return filter, andthe mid way of the connecting pipe line of theaccumulator
pH value, chloride ion, hardness, residue oftranspiration, and general bacteria.
See Fig 3.14.

60000
Reservoir
タンク

50000

Filter
フィルタ

40000

Acc.

30000
20000
10000
0
0

400
800
Time
(h)
運転時間(hr)

1200

1600

Fig. 3.14 Water quality evaluation results (30℃) (Measured values)21

7
Reservoir
タンク
Filter
フィルタ

6

Acc.

蒸発残留物(mg/l)

pH値
PH

8

Transpiration residue (mg/ℓ)

9500
Reservoir
タンク

400

Filter
フィルタ

Acc.

300
200
100
0

5
0

400

800

1200

0

1600

Time (h)
運転時間(hr)

1600

200

300
Reservoir
タンク

250

Chloric ion (mg/ℓ)
塩素イオン(mg/l)

Hardness(mg/ℓ)
硬度(mg/l)

400
800
1200
Time (h)
運転時間(hr)

Filter
フィルタ

200

Acc.

150
100
50

Reservoir
タンク

160

Filter
フィルタ

Acc.

120
80
40
0

0
0

400

800
1200
Time (h)
運転時間(hr)

1600

0

400

800
1200
Time (h)
運転時間(hr)

1600

Fig. 3.14 Water quality evaluation results (30℃) (Measured values)

22Chapter 3 Operating Aqua Drive System
3.2.2 Control and maintenance of water quality
(3)
(1)

(2)

(3)
(4)

Filtration equipment: To eliminate substances causing contamination,
bacteria, and other microbe organic substances, the filtrationequipment shall be equipped with lines such as the water supply line,
the return line, the suction line, and so forth, if necessary. The
system is desirably designed so that it enables to monitor the clogging
of such filters.
Water supply filter: The water supply filter should be equipped at theinitial stage of operation and when the water is supplied for maintaining
the water level.
Replacement of the working fluid: The working fluid should be
replaced according to frequency of the use and the operational
environment.
Service: Periodical service should be done to the air breather andfilters to keep them clean.

Temperature control: If operating the system within the proper
temperature range is difficult, proper countermeasures should be taken
according to situations. The working fluid will be frozen at 0 ℃.
Therefore, when the system is used in cold climates or where theambient temperature may become 0 ℃ or lower, installing someheating equipment will be required to prevent the fluid from being
frozen at any place in the system. Contrary, when the system is used
where the working fluid may be evaporated due to the temperature riseof the reservoir, modifying the reservoir shape and size or installingheat exchangers will be required. Especially, the countermeasure forplaces where the working fluid does not circulate, such as the cylinderand rotary oscillating torque actuator, is important.

3.2.3 System operation temperature
(1)

(2)

23

Temperature of the system: To prevent the freezing and to restrain
the generation of vapor, the water temperature should be + 5 ℃ to
45 ℃.
Temperature of the components: When operation temperature is
specified by each component manufacturer, the component should be
used within such a specified temperature. When the user decides theoperation temperature for the system, this point should be considered.
Note that the temperature of surfaces of each component should
always be touchable by the human being.

M
T (℃)
Fig 3.15 Experimental apparatus for observing the effect of cooler

If the water temperature exceeds the specified temperature range, usea cooler. As shown in Fig 3.15, the experiment was performed toobserve the effect of the cooler. The water ejected from the pumpruns through a valve. Then, the water returns to a reservoir via acooler after flowing through the valve. When the valve is throttled, thepressure loss that is generated by throttling the valve heats up thewater. In addition, the power loss at the pump also becomes thecause of heating.



The circles in Fig 3.16 indicate the measurement result of the changeof the reservoir temperature per run time when the cooler is not used.
It shows that when the water quantity in the reservoir is small, the risingrate of the temperature becomes higher.

The triangles indicate the measurement result of the water temperaturewhen the water quantity is small (0.025 m3) and the cooler is used. Itshows that using the cooler helps the water temperature to be within
the specified temperature range. Both the solid and broken lines
indicate the calculated water temperature with considering the heatbudget of the circuit.

The specific heats of the water and working oil are different
C p ( J / kgK)) : 4180 for the water and 2018 for the oil. The specificheat of the water is large about as twice as that of the oil. Accordingly,
if the same amounts of heat are heated up, the rising rate of the watertemperature is a half of the counterpart of the working oil.

3

Small tank (0.025m ) without cooling

50
3

T (℃)

Large tank (0.1 m )without cooling

40
3

Small tank (0.025 m )with cooling (9 L/min)

30
0

20

40

60

t (min)Fig 3.16 Differences of the water temperature riseand effects of cooler per reservoir size

80

24

Chapter 3 Operating Aqua Drive System
3.2.4 Effectiveness of cooler(Requirements）
Model of the heat exchanger: TCW-106-2
Temperature of the cooled fluids at the inlet: 45 ℃.
Temperature of the cooled fluids at the outlet: 42℃.
Temperature of the cooling water at the inlet: 27 ℃.
Flow rate of the cooling water: 9  /min

18000

Exchanged
heat KJ/h
交換熱量 ｋＪ／ｈ

16000
14000

Tap
water
水道水

10000

Fig. 3.17 shows the passing flow rate and the exchanged amount of heat
when the tap water and the mineral working oil are cooled down by the heatexchanger

8000

The exchanged amounts of heat are expressed as follows:

12000

6000

Hc  po  Co  Qo  T  60 (oil),4000

pw  Cw  Qw  T  60 (water).

Oil油圧作動油
hydraulic working fluid

2000
0

0

5

10

15

20

25

30

 /minPassing flowrate of the cooled fluidl/min
被冷却流体の通過流量

Fig. 3.17 Relationship between the flow rates of the cooled fluids
and the exchanged amounts of heat

Data and the heat exchanger presented in this page are supplied
by TAISEI KOGYO CO., LTD.

25

35

The exchanged amount of heat of tap water is about 2.5 times greaterthan that of the oil due to the water’s property. It means that the cooler for
the ADS can be more compact than that for the working oil of mineral oils.

3.3 Other issues(1)

Avoidance of the dry
operation

To avoid damages due to the dry operation, the pump should be always operated with the working fluid supplied.

(2)

Ventilation

At the very first operation of the system, the air of the water hydraulic unit, pipes, actuator, etc., must be completely
evacuated to protect the components and obtain the required performances.

(3)

Monitoring of the filter
pressure loss

Proper filtration of the working fluid not only extends the lifetime of the water hydraulic components, but also is important
to demonstrate the maximum performance of the system. Therefore, the system is desirably designed so that themonitoring of the filter pressure loss is allowed.

(4)

Flushing

To prevent troubles due to entry of foreign substances into the working fluid, oils and dirt attached on the pipes, couplings,
and components shall be sufficiently removed before integrating them into the system. In addition, to remove suchforeign substances in the water hydraulic unit and the pipes, flushing shall be done when the system is operated anew.
The water temperature should be kept higher within the operational range during the flushing to improve the effect.

(5)

Pulsation and noiseof the triple plungerpump

As the triple plunger pump is mainly used at the lower rotational speed, troubles may occur to the system due topulsation. Therefore, the pulsation-prevention measures should be taken on the accumulator and rubber pipes.
Otherwise, the system should be configured with the pump unit separated.

(6)

Storage of thecomponents and unit

The user should follow the instructions provided from the suppliers when the user stores the components and unit. Many
overseas manufacturers fill the non-freezing solution for the purpose of preventing freezing and the components interior
surface from rusting during storage and preservation (e. g., mono propylene glycol). When the system is operated anew,
the non-freezing solution should be sufficiently washed away.

(7)

Periodical inspection

Vibration generated from the pump may loosen the pipe connecting elements. To prevent the working fluid leakage andthe air suction, the periodical inspection should be performed to check and re-tighten the joint parts and screws of thepipes.

26

Chapter 4 Application of Aqua Drive System
The applicable environment and promising applicable range in the future
are listed below.
(1)

(2)

(3)

(4)

Production and manufacturing environment for which
Food processing
cleanness and sanitation are required:machinery, food and drink wrapping and canning machinery,
production lines for semiconductor and information devices, medical
and pharmaceutical production lines, general production andprocessing machinery for cleaner and better work environment
Working environment for which the natural environment
preservation has to be considered: Machinery operated on
offshore and rivers, operating systems for sluice gates and others,machinery operated underwater and undersea
Specialized atmosphere environment such as the radioactive
atmospheric field of atomic energy: Inspection and repairing
machinery for the internal reactor core, demolition machinery
Environment for human beings which requires the fire
protection and safety: Devices and tools for fire fighting andrescue, machinery for medical and social welfare services andfacilities for housing for the senior, sports gear and leisure equipment,
mobile stages

In recent years, instructions and regulations base on the law, particularly
ISO9000, ISO14000, and HACCP (Hazard Analysis Critical Control Point),
have increasingly penetrated. In such a background, significance of theaqua drive technology has also been increasingly recognized as a mean toacquire such certification. In addition, on the base of the superior fluid
power driving property that is described in Chapter 3, expectation to the
ADS has been rising as the fundamental technology to achieve the“emission free” policy of each kind of production machines.

Figure 4.1 visualizes the whole concept of ADS. It contains thefundamental technology, which supports the “aqua drive technology”,
accessories, which are necessary to configuration of the system, andapplicable environments and promising fields of application as mentioned
above.

YIELDUS(Automated poultry breast deboner)

TORIDAS(Automated poultry thigh deboner)
Photographs: Courtesy of MAEKAWA MFG. CO., LTD.

27

Fig. 4.1 Applicable fields of ADS and their supporting technologies

28

Chapter 4 Application of Aqua Drive System

29

JFPA Water Hydraulics Committee Members (Alphabetical order):Contact JFPA regarding context of this book or the products shown.
EBARA RESEARCH CO., LTD.
4-2-1 Honfujisawa, Fujisawa-shi
Kanagawa 251-8502 Japan
Phone: +81-466-83-7111
Fax: +81+466-82-2630

KAYABA INDUSTRY CO., LTD.
World Trade Center Bldg.
2-4-1, Hamamatsu-cho
Minato-ku, Tokyo 105-6125 Japan
Phone: +81+3-3435-3581
Fax: +81-3-3436-6759

KITAMURA SHOKO CO., LTD.
2-1-7 Motoasakusa
Taito-ku Tokyo 111-0041 Japan
Phone: +81-3-3843-3218
Fax: +81-3-3843-2718

NABCO LTD.
2-21, Isogami-Dori 2-chome
Chuo-ku, Kobe 651-0086 Japan
Phone: +81-78-251-8106
Fax: +81-78-251-8090

NACHI-FUJIKOSHI CORP.
World Trade Center Bldg.
2-4-1, Hamamatsu-cho
Minato-ku, Tokyo 105-6125 Japan
Phone: +81+3-3435-5111
Fax: +81-3-3436-6366

SAKAGAMI SEISAKUSHO LTD.
4-17-6, Kinshi
Sumida-ku, Tokyo 130-0013 Japan
Phone: +81-3-3625-1111
Fax: +81-3-3625-8270

TAKAKO INDUSTRIES, INC.
3-1-48, Nunoichi-cho
Higashi-Osaka-shi
Osaka 579-8004 Japan
Phone: +81-729-88-2622
Fax: +81-729-88-2920

TOYOOKI KOGYO CO., LTD.
45 Aza-Kaizan, Hatchi-cho
Okazaki-shi, Aichi 444-3592 Japan
Phone: +81-564-48-2311
Fax: +81+564-48-7908

YAMAMOTO SUIATSU
KOGYOSHO CO., LTD.
2-8-8 Shomoto-scho
Toyonaka-shi, Osaka 561-0835
Japan
Phone: +81-6-6331-4651
Fax: +81+6-6331-2516

YUKEN KOGYO CO., LTD.
Hamamatsucho Seiwa Bldg.
4-8 Shiba Daimon 1-chome
Minato-ku, Tokyo 105-0012 Japan
Phone: +81-3-3432-2110
Fax: +81-3436-2344

30

Reference
Special Acknowledgement to:
Sophia University
Mechanical Engineering Dept.
Kioicho 7
Chiyoda-ku, Tokyo 102-0094 Japan
Phone: +81+3-3238-3302
Fax: +81-3-3238-3311

Yokohama National University
Department of Production
Engineering, Faculty of Engineering
156 Jobandai, Hodogaya-ku
Yokohama-shi, Kanagawa 240-0067
Japan
Phone: +81+45-335-1451
Fax: +81-45-331-6593

This project is made possible by the promotion
grant for machinery-related industries offered by
the Japan Motorcycle Racing Organization.

31

Japan Fluid Power Association
Kikai Shinko Bldg., Room 311
3-5-8 Shiba-koen,
Minato-ku, Tokyo 105-0011 Japan
Phone: +81+3-3433-5391
Fax: +81-3-3434-3354