Enhanced solid piston flow controller

A flow control valve (10) is provided including a valve body (20) and a piston (16). The valve body (20) has extending therethrough a longitudinal bore (18) defining a fluid passage (32). The piston (16) is slidably disposed within the bore (18) to vary the flow area of a fluid flow through the control valve (10). The piston (16) has a generally cylindrical body formed from a solid piece of material. The piston (16) contains a longitudinal flow channel (24). The longitudinal flow channel (24) has a varying depth. The piston (16) preferably slides within the longitudinal bore (18) to vary the flow area of the fluid passage (32) such that the fluid flow through the control valve (10) is substantially constant over a selected range of pressure differentials across the control valve (10).

TECHNICAL FIELD OF THE INVENTION 
The present invention pertains in general to flow control valves and more 
particularly to an automatic flow control valve having a solid flow 
control piston. 
BACKGROUND OF THE INVENTION 
Constant flow control valves have numerous applications in piping networks. 
For example, in a building air conditioning and heating system, water or 
other liquid at an appropriate control temperature may be pumped from a 
central station through a piping network to various heat exchanger units 
located throughout the building. Some of these heat exchanger units are 
located relatively close to the central station while others are located 
much farther away. The fluid pressure applied across inputs and outputs of 
the respective heat exchanger units varies widely because of factors such 
as frictional losses inherent in the flow of the liquid through the piping 
network and the distances the liquid must travel from the central station. 
The flow rate in each branch of the network is a direct function of the 
pressure drop existing across that branch. Two contributors to the 
existence and magnitude of the pressure drop are line friction and 
equipment pressure drop. The actual pressure drop in one branch is often 
different from the original desired, or designed, value, leading to a flow 
rate in that branch which is different from the desired flow rate. Changes 
from the desired flow rate in one branch will influence the flow rate in 
other branches. To obtain the desired flow rate in the various branches of 
such a network, the network should be hydraulically balanced. 
Hydraulic balancing often involves adding additional pressure to one or 
more branches within the system, a measure which may create wasteful 
pressure drops therein. Pumps are frequently oversized to provide the 
additional pressure required to balance the network. Because these pumps 
are frequently operated at flow rates and pressures other than their 
optimum performance conditions, wasteful energy consumption results. 
Constant flow control valves help alleviate the need for hydraulic 
balancing. Examples of such control valves are disclosed in U.S. Pat. No. 
4,766,928 issued to Golestaneh and U.S. Pat. No. 5,174,330 issued to 
Golestan et al. Both references disclose a constant flow rate control 
valve including a movable piston having a plurality of side ports and an 
orifice on an end wall of the piston. Pressure differential across the 
valve moves the piston against a resilient spring to expose an appropriate 
portion of the side port area to maintain a constant flow rate at that 
pressure differential. There is a minimum pressure differential required 
for the flow rate to increase for establishing the desired flow rate for 
the Golestaneh, Golestan et al. and other prior control valves. For some 
systems, particularly those with long piping runs, even this minimum 
pressure drop may not be attainable. For high volume flows, reaching this 
minimum is costing energy usage. 
In the previously known constant flow control valves, a variable orifice 
regulates the fluid flow. In these constant flow control valves, the 
variable orifice is distributed along the outside of a hollow piston. As 
the differential pressure increases, a portion of the orifice moves below 
the shoulder which reduces the flow passage area. For small flow rates, 
this distribution of the passage along the entire length of the hollow 
piston requires that it become extremely narrow. Because the port is so 
narrow, a small variation in width may be relatively significant and cause 
a significant variation in the flow rate. Also, with this type of valve, 
there is some fluid that flows between the outside of the piston and the 
shoulder which is affected by manufacturing variations in the piston and 
shoulder. For a given manufacturing variation in the diameter of the 
piston, the variation in the flow rate between the outside of the piston 
and the shoulder is typically proportional to the perimeter of the piston. 
Another problem with prior control valves is that they may cause internal 
local disturbances near the piston as the fluid passes through the 
regulating orifice; these disturbances may reduce the energy of the fluid 
flow. Still another problem with prior control valves is that their parts 
and orifices may become clogged with fluid borne particles or have 
deformities which may alter the respective control valve flow 
characteristics. Furthermore, prior control valves may have parts with 
critical dimensions which may require the valve to be expensively 
manufactured by high precision machinery. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, the disadvantages and problems 
associated with previous flow control valves for regulating fluid flow 
rate have been substantially reduced or eliminated. The present invention 
provides a flow control valve including a valve body and a piston. The 
valve body has a longitudinal bore extending therethrough to define in 
part a flow passage. The piston is slidably disposed within the bore to 
vary the fluid flow area of the flow passage through the control valve. 
The piston has a generally cylindrical configuration formed from a solid 
piece of material. The piston preferably contains a longitudinal flow 
channel formed in the exterior of the piston, the longitudinal flow 
channel having an up stream end and a down stream end for communicating 
fluids therethrough. The piston preferably slides within the longitudinal 
bore to vary the flow area of the flow passage such that the fluid flow 
through the valve is substantially constant over a selected range of 
pressure differentials across the control valve. 
One aspect of the present invention includes a control valve having a valve 
body with a longitudinal bore extending therethrough and a piston slidably 
disposed in the longitudinal bore. A longitudinal flow channel is formed 
in the exterior of the piston and has an up stream end and a down stream 
end for communicating fluids therethrough. An annular shoulder is 
preferably formed within the valve body adjacent to the exterior of the 
piston intermediate the up stream end and the down stream end of the 
longitudinal flow channel whereby the annular shoulder cooperates with the 
longitudinal flow channel of the piston to regulate fluid flow through the 
longitudinal bore. The longitudinal flow channel preferably has a varying 
depth. 
The present invention provides numerous technical advantages. A technical 
advantage of the present invention may include providing for lower energy 
loss across the associated control valve. 
Another technical advantage of the present invention may include providing 
a significant reduction in the disturbance of the flow field as the fluid 
flows through the associated control valve. 
Another technical advantage of the present invention may include providing 
a reduced tendency to clog with particles carried by the fluid and a 
greater tolerance of clogs or deformities which may effect the fluid flow 
through the associated control valve. The flow regulating path associated 
with the piston of the present invention is not the small, narrow opening 
that may have made previously known valves sensitive to manufacturing 
variations and more likely to clog. 
Another technical advantage of the present invention may include that the 
solid piston may be manufactured by standard precision tooling with a 
longitudinal flow channel having a variable depth to provide the desired 
flow characteristics for the associated control valve, i.e., without 
exotic machining. 
Another technical advantage of the present invention may include that the 
longitudinal flow channel defines a flow passage which is substantially 
parallel with the fluid flow through the control valve. The present 
invention allows both the depth and width of the longitudinal flow channel 
to be selected to optimize performance of the associated control valve. 
Another technical advantage of the present invention may include providing 
a reduction in the leakage of fluid around the perimeter of the piston in 
the associated control valve by reducing the piston perimeter. This and 
other features make the present invention particularly suitable for 
extremely low flow rate control. 
Yet another technical advantage of the present invention is that the piston 
may be solid as opposed to hollow. Hollow pistons typically require a 
larger diameter to provide a flow path through the piston. The solid 
piston that may be used with the present invention allows for a smaller 
diameter which in turn reduces the influence of manufacturing variations 
on fluid flow between the shoulder and the piston since the effect of such 
a variation is directly proportional to the perimeter of the piston. 
Furthermore, because the piston may be solid, it may have additional 
strength.

DETAILED DESCRIPTION OF THE INVENTION 
The preferred embodiment of the present invention and its advantages are 
best understood by referring to FIGS. 1-4C of the drawings, like numerals 
being used for like and corresponding parts of the various drawings. 
Referring to FIG. 1, flow control valve 10 is shown disposed within 
longitudinal bore 12 of a housing 14. Housing 14 may be of a Y-pattern or 
any other suitable configuration. In some configurations, housing 14 may 
not be necessary. The general direction of the fluid flow in longitudinal 
bore 12 is shown by the arrows to be from right to left for the 
orientation shown. For purposes of illustration only, housing 14 is shown 
with a generally hollow, tubular configuration. Longitudinal bore 12 may 
be formed in a wide variety of housings having various configurations such 
as rectangular or square. Also, multiple longitudinal bores 12 and flow 
control valves 10 may be disposed in the same housing (not shown). 
Flow control valve 10 includes a flow control piston 16 slidably disposed 
within a longitudinal bore 18 of a valve body 20. Valve body 20 has an 
interior wall 36 and an exterior wall 37. Flow control piston 16 has a 
longitudinal flow channel or slot 24. Channel 24 as shown has a varying 
depth and uniform width. For some applications more than one channel 24 
may be formed in the exterior of piston 16. For other applications channel 
24 may be formed with both a varying depth and varying width. 
Piston 16 has a generally cylindrical body formed from a solid piece of 
material. Bore 18 provides a fluid passage 32 which receives at an up 
stream or first opening 34 fluid flowing through channel 24. The fluid 
then exits fluid passage 32, defined in part by bore 18, and down stream 
or second opening 38. 
As the fluid flows through bores 12 and 18, a pressure differential is 
formed across flow control valve 10. A biasing means, such as spring 39, 
responds to this differential pressure by regulating the longitudinal 
position of piston 16 within bore 18 with respect to valve body 20. By 
adjusting this position, spring 39 varies the flow area associated with 
piston 16 (the effective flow area of channel 24) to maintain a 
substantially constant flow rate through flow control valve 10. 
As discussed in more detail below, channel 24 significantly reduces the 
disturbance of the flow field as fluid flows through flow control valve 
10. Additionally, the varying depth of channel 24 makes flow control valve 
10 much more clog tolerant and resistant than prior flow control valves. 
Furthermore, irregularities along the length of channel 24 dimensions have 
less affect on the flow control characteristics than do irregularities in 
the dimensions of prior orifice type flow control valves. 
For example, as piston 16 fully retracts into valve body 20 (FIGS. 4B and 
4C), the effective flow area of control valve 10 is that of channel 24 
(channel width.times.depth) at the external edge of annular shoulder 64. 
The width and depth of channel 24 are preferably large enough to be easily 
milled by standard tooling machines. Forming channel 24 with a uniform 
width will reduce manufacturing costs. Any irregularity (i.e., bumps, 
pits, etc.) along the walls or bottom of channel 24 affects the flow 
characteristics of valve 10 primarily when the portion of channel 24 
containing the irregularity is positioned adjacent to annular shoulder 64. 
Fluid simply bypasses the irregularity when the irregular channel portion 
is positioned either up stream or down stream from annular shoulder 64. 
Referring again to FIG. 1, a retainer or snap ring 40 is provided for 
releasably anchoring flow control valve 10 within longitudinal bore 12 in 
a predetermined position relative to housing 14. Housing 14 may then be 
coupled on each end to a pipe or conduit (not shown) through which the 
fluid flows. In other embodiments, however, flow control valve 10 may be 
installed directly into a conduit without a housing. Retainer ring 40 may 
be installed in a groove 42 formed in the interior wall of housing 14. 
Once installed, retainer ring 40 engages the up stream end of valve body 
20 to limit up stream movement of valve body 20. 
Similarly, a shoulder 44 on the exterior of valve body 20 engages a 
shoulder 46 on the interior of housing 14 to limit the movement of flow 
control valve 10 in a down stream direction. Thus, an exterior portion 48 
of valve body 20 is anchored between retainer ring 40 and shoulder 46. 
Groove 50 is preferably formed around exterior portion 48 of valve body 20 
for holding seal means or O-ring 52. Seal means 52 forms a fluid barrier 
with the adjacent surfaces of valve body 20 and housing 14 between the up 
stream and down stream ends of flow control valve 10. Thus, seal means 52 
directs all fluid flow within housing 14 through flow control valve 10. 
Spring 39 is disposed within bore 18 for urging flow control piston 16 in 
an up stream direction toward a fully extended position. One end of spring 
39 is seated against an interior shoulder 56 formed at the down stream end 
of piston 16. The other end of spring 39 is seated against a shoulder 58 
of a spring retainer 60. Up stream shoulder 62 of piston 16 engages 
annular shoulder 68 of valve body 20 to limit the movement of piston 16 in 
the up stream direction. 
The end of bore 18 adjacent down stream opening 38 is threaded to receive 
spring retainer 60, which has threads cut along a portion of its exterior. 
Retainer 60 is rotatable within bore 18 to vary the compression of spring 
39. Varying the compression of spring 39, "fine tunes" or adjusts the 
designed flow rate over which flow control valve 10 maintains a 
substantially constant flow rate substantially equal to the designed flow 
rate (i.e., the selected range). Typically, this fine tuning is done 
during the manufacturing and assembly process to bring flow control valve 
10 to within desired tolerances for the desired flow rate regulation. 
Channel 24, annular shoulder 64 and spring 39 cooperate to maintain a 
substantially constant rate of fluid flow through fluid passage 32 over 
the selected range of pressure differentials across flow control valve 10. 
A graph of flow rate versus pressure differential for a prior flow control 
valve is shown in U.S. Pat. No. 5,174,330, issued to Golestaneh et al. on 
Dec. 29, 1992, which is hereby incorporated by reference for all purposes. 
In the present invention, channel 24 lowers the minimum flow rate 
attainable for a given differential pressure by concentrating the flow 
area. Fluid flow through channel 24 is essentially parallel with fluid 
flow in both bore 12 and fluid passage 32. 
Referring to FIG. 2, flow control piston 16 is shown in more detail. Piston 
16 is formed from a generally solid cylinder 66. Piston 16 has a down 
stream end 72 with an enlarged diameter forming shoulders 56 (FIG. 1) and 
62. Down stream end 72 has a generally cylindrical shape compatible with 
the dimensions of bore 18, with the exception of flat sides 76a and 76b 
and a cut-out 78. Piston 16 also has an up stream end 74 with a diameter 
smaller than that of down stream end 72. 
An advantage provided by the diameter of up stream end 74 is that it is 
smaller than the diameter of pistons used in prior control valves. 
Ideally, a control valve forces fluid to flow through only the channels or 
orifices in a piston designed for passage of the fluid. In actual 
operation, however, fluid often leaks through a control valve along the 
perimeter of the piston. The perimeter of a piston is directly related to 
the piston's diameter. That is, if a piston has a larger diameter, it will 
have a larger perimeter. Thus, because flow control valve 10 has piston 16 
with a smaller diameter at up stream end 74 than prior control valves, the 
leakage of fluid associated with the perimeter of the piston is reduced. 
Flow channel 24 is formed along the exterior of cylinder 66 extending 
longitudinally from down stream end 72 to up stream end 74. In the 
embodiment represented by FIGS. 1-4C, piston 16 is shown having a single 
channel 24 on the exterior of cylinder 66. However, other embodiments of 
piston 16 may have more channels 24, which may or may not be symmetrically 
spaced on the exterior of cylinder 66, as the desired flow rate design 
dictates. Channel 24 preferably has a width equal to or less than one-half 
the diameter of cylinder 66 adjacent to up stream end 74. The width of 
channel 24 remains substantially constant from the end adjacent to up 
stream end 74 to the end adjacent to down stream end 72. Also, channel 24 
is shown as having a varying depth throughout. The depth of channel 24 is 
relatively shallow at the end adjacent to up stream end 74 as opposed to 
the end adjacent to down stream end 72. In between its two ends, the depth 
of channel 24 tapers from the down stream depth to the up stream depth. 
Other embodiments may have bottoms of varying contour to alter the flow 
characteristics of piston 16. Because the flow area associated with 
channel 24 is substantially perpendicular to the fluid flow through 
channel 24, this flow area increases in an up-stream-to-down-stream 
direction. 
The dimensions of channel 24 (end depths and width) and length of piston 16 
depend upon the predetermined flow control range and designed flow rate of 
flow control valve 10. These dimensions and this length are respectively 
calculated using well known mathematical formulas which describe fluid 
flow as a function of pressure differential and effective flow area. 
Cut-out 78 is provided in down stream end 72 to prevent or minimize 
disturbance in the flow field as fluid exits channel 24. 
Referring to FIG. 3, flow control piston 16 is shown disposed within a 
portion of valve body 20 and housing 14. Spring retainer 60 and spring 39 
are not illustrated. Down stream end 72 of piston 16 has a diameter 
roughly equal to the diameter of interior wall 36 of valve body 20. 
Flat sides 76a and 76b facilitate machining of piston 16 and channel 24. If 
down stream end 72 was essentially circular except for cut-out 78, piston 
16 would need to be tightly held within a vise to keep piston 16 from 
rotating during manufacture, such as when channel 24 is cut into cylinder 
66 of piston 16. However, piston 16 could be deformed if the vise is too 
tight. Flat sides 76a and 76b allow piston 16 to be securely held during 
machining, without causing deformation of piston 16. Flat sides 76a and 
76b also help identify the location where channel 24 is to be cut. 
Referring generally to FIGS. 4A-C, the operation of flow control valve 10 
is now discussed. In general, a fluid flows into the effective flow area 
defined by channel 24 and shoulder 64 and out through cut-out 78 or around 
flat sides 76a and 76b (FIG. 3), into fluid passage 32 (FIG. 1) and exits 
through down stream opening 38. The effective flow area of channel 24 is 
the only opening (in a plane perpendicular to the fluid flow) exposed on 
the up stream side of annular shoulder 64. That is, annular shoulder 64 
cooperates with cylinder 66 of piston 16 to force virtually all fluid flow 
through channel 24. 
Referring to FIG. 4A, when the pressure differential across flow control 
valve 10 is at or below the minimum pressure required to enter the 
selected range, spring 39 urges piston 16 to a fully extended (i.e., low 
differential pressure) position with respect to bore 18. In this fully 
extended position, the maximum flow area of channel 24 is available for 
fluid flow. As the pressure differential falls below the minimum, the flow 
rate will fall too. Shoulders 62 and 68 prevent piston 16 from extending 
further to increase the effective flow area and compensate for the 
pressure drop. 
Still referring to FIG. 4A, as the pressure differential increases beyond 
the required minimum pressure, piston 16 is forced to retract into bore 18 
until the force exerted on piston 16 by spring 39 in the up stream 
direction equals that exerted by the fluid flow in the down stream 
direction. As piston 16 retracts, the effective flow area of channel 24 is 
reduced. Thus, when the fluid differential pressure force equals the 
spring force, piston 16 is in a partially extended or intermediate flow 
control position where the effective flow area of flow control valve 10 is 
such that a substantially constant flow rate through control valve 10 is 
maintained. The variable depth of channel 24 is a major factor in 
determining the position of piston 16. 
Referring to FIG. 4B, as the pressure differential across flow control 
valve 10 increases further, the effective flow area of channel 24 is 
reduced even more. Thus, as piston 16 is retracted, the change in the 
effective flow area (required to keep the flow rate constant) is 
attributable primarily to a change in the position of piston 16 and 
channel 24 relative to shoulder 64 which corresponds to the depth of 
channel 24. 
Referring to FIG. 4C, as the pressure differential reaches the maximum 
pressure of the selected range, piston 16 is in a fully retracted (i.e., 
high differential pressure) position with respect to bore 18; the 
effective flow area is reduced to a minimum, although there is still fluid 
flow into channel 24. As the pressure differential increases beyond the 
maximum, the flow rate will increase, because piston 16 may retract no 
further to vary the flow area to maintain a substantially constant flow 
rate. It is understood that in most applications, flow control valve 10 
will have a selected range of pressure differentials which is large enough 
to encompass expected maximum and minimum pressure differentials within 
the fluid system in which it is installed. 
Valve 10 with channel 24 provides numerous advantages over prior control 
valves. For example, by providing a flow path which is substantially 
parallel to the flow path through the conduit (not shown) and bore 12, 
channel 24 reduces the amount of disturbance in the flow field generated 
as fluid flows through control valve 10. That is, as fluid flows from the 
shallow end of a channel 24 into up stream opening 34 of valve body 20, 
the fluid is not required to sharply turn. Channel 24 allows the fluid to 
flow into up stream opening 34 in a path substantially parallel to the 
natural flow path of the fluid through the conduit. Prior control valves 
often contain channels in which fluid must flow into side orifices at a 
substantially perpendicular angle from the natural flow path. In the 
present invention, therefore, less disturbance in the flow field is 
created than if the fluid was required to enter a side orifice at a sharp 
angle. 
A reduction in disturbances in the flow field provides advantages. Because 
less disturbance is generated, less kinetic energy is lost. That is, 
because the fluid enters up stream opening 34 in a path parallel to the 
natural flow path, disturbances in the flow field and, hence, loss of 
kinetic energy, are reduced. 
Another advantage provided by the valve 10 with varying-depth design of 
channel 24 is a reduction in the likelihood that a fluid borne particle 
will lodge itself within channel 24. Because channel 24 deepens toward its 
down stream end, a fluid borne particle is typically forced toward a 
deeper portion, not a shallower portion, until the particle passes into 
fluid passage 32. Even if a particle does become wedged in channel 24, the 
particle may not significantly effect the flow control capability of valve 
10. The fluid will typically flow over the wedged particle and back into 
channel 24. The same is true for a deformity in channel 24. The fluid will 
simply flow around the deformity and back into the non-deformed down 
stream portion of channel 24. Also, a particle may wedge between valve 
body 20 and channel 24 when piston 16 is in an intermediate flow control 
position. However, control valve 10 will typically purge itself of the 
particle when piston 16 returns to a substantially fully extended position 
(during times when there is reduced differential pressure across valve 
10), whereby the particle will typically dislodge and exit through fluid 
passage 32. 
Still another advantage is that because of the flow control provided by 
channel 24, the smallest dimensions of channel 24 are typically larger 
than those of prior channels for a given flow rate design; these larger 
dimensions of channel 24 are more easily machined with standard precision 
machine tools. For example, the depth and width of channel 24 define its 
flow area. Since the effective flow area of flow channel 24 is located at 
annular shoulder 64, rather than extending along the entire cylinder 66 of 
piston 16, extremely narrow ports are not required as with many prior 
pistons. Also, because flat sides 76a and 76b facilitate machining of 
piston 16 (as explained before), channel 24 may be easily fabricated with 
standard precision machine tools. 
A further advantage provided by channel 24 is that it typically extends the 
entire length of piston 16. This extension provides for a variable 
effective flow area along the entire length of piston 16. Prior pistons 
often have only side ports which do not extend the length of the piston. 
Thus, prior pistons provide for a variable effective flow area only along 
the portion of the piston integral with the side ports. 
Although the present invention and its advantages have been described in 
detail, it should be understood that various changes, substitutions and 
alterations can be made therein without departing from the spirit and 
scope of the invention as defined by the appended claims.