Variable volume peristaltic pump

A peristaltic pump driven by a single speed power source has a fixed length of flexible wall tubing circumferentially positioned between the wall of the inner chamber and an adjustable band. The flexible band has one end fixed to the pump housing and the other to an adjusting screw. Turning the adjusting screw varies the effective length of the adjustable band and consequently the degree of contact with the flexible wall tubing. Increasing the effective length of the adjustable band flattens the tubing against the wall, thereby changing the volumetric capacity of the tubing and delivery rate of the pump. Decreasing the effective length of the adjustable band has the opposite effect.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to peristaltic pumps driven by a single speed 
power source and in particular to peristaltic pumps whose volumetric 
delivery rate is adjustable. 
2. Description of the Prior Art 
A peristaltic pump consists of a flexible tube within a housing having an 
arcuate chamber where a flexible tube is circumferentially compressed by a 
series of rollers or an eccentric against the wall of the inner chamber. 
As the rollers move along the tube, they force fluid through the tube. The 
displacement of fluid or the delivery rate of a peristaltic pump is 
determined by the flexible tubing diameter, the motor speed and any gears 
between the motor and the pump rollers. 
In the prior art, peristaltic pumps have been in use since at least 1891. 
The Burson U.S. Pat. No. 460,944, issued in 1891 shows an example of a 
peristaltic pump of that period. A list of some of the prior art since 
1891 showing the general principles of peristaltic pumps is as follows: 
______________________________________ 
Oliveras U.S. Pat. No. 1,741,070 
Santiago et al 1,988,337 
Knott 2,314,281 
Wittenberg 2,403,572 
Bogoslowsky 2,414,355 
Vogel et al 2,885,967 
Simer et al 2,930,326 
Daniels 2,955,543 
Seyler 2,977,890 
Brkich 3,067,692 
Worth et al 3,358,609 
Muller 3,384,080 
Jess 4,155,362 
______________________________________ 
The flexible tubing used in peristaltic pumps is important since it is the 
heart of the pump and has to sustain stresses from repeated flexing and 
abrasion due to the repeated contact with the rollers. Under repeated 
flexing and abrasion the flexible tubing will fail and fracture, causing 
leakage. A characteristically short tubing life is perhaps the most 
serious drawback to using peristaltic pumps more generally, and has 
severely limited the range of present applications. This problem has been 
recognized and explored in a number of prior art patents which attempt to 
prolong the tubing life by redesigning the tubing. 
______________________________________ 
Seyler U.S. Pat. No. 2,693,766 
Mascaro 2,917,002 
Mascaro 2,925,045 
Murray 2,987,004 
Vadot 3,192,863 
Fitter 3,875,970 
Gerritsen 3,887,306 
LeGeay, nee Lechat et al 
4,080,113 
Gerritsen 4,110,061 
______________________________________ 
Peristaltic pumps have an economic advantage over other types of pumps and 
the added cost of specifically designed tubing would take away some of 
this advantage. Further, the tubing of the prior art will eventually fail 
and need to be replaced. The risk of failure, cost of down time and the 
replacement cost of the prior art specially designed tubing will detract 
from the economic advantage that peristaltic pumps have over other pumps. 
Another approach in lengthening the life of the flexible tubing is to use a 
buffer material between the flexible tubing and the rollers. The Stanber 
U.S. Pat. No. 3,583,838 shows a flexible ring 17 in FIG. 2 that seals the 
roller bearing of the eccentric roller of the pump. The ring 17, however, 
does not actually act as a buffer but acts with the roller in contacting 
the tubing as described previously. The abrupt and highly localized 
longitudinal stresses resulting in the tubing's wall generally caused by 
direct roller contact are not avoided. The Shlisky U.S. Pat. No. 3,591,319 
teaches a conduit protective member between a plurality of rollers and the 
flexible tubing. However, in order for the conduit protective member to 
act as a buffer, the flexible conduit is stretched over the rollers 
sufficiently for occlusion to take place and for the flexible conduit to 
lie against the protective member in such frictional engagement so as to 
prevent wandering and eliminate any longitudinal stretching and abrasion 
of the flexible conduit. As a result of tightly extending the flexible 
conduit over the rollers, other stresses are introduced that offset any 
gain obtained by the protective member. The Gelfand U.S. Pat. No. 
3,723,030 shows a plurality of tubes, each protected from the rollers by a 
nylon strip. This protective strip offers minimal protection to the tubing 
since it merely eliminates the contact with the roller and does not reduce 
the severity of the stress caused by the rollers. 
Further, all the protective strips in the prior art are susceptible to 
abrasive wear, creep, and eventual failure from the constant action of the 
rollers. The failure of the protective strips results in either direct 
contact between the rollers and the flexible conduit or in creating the 
situation where the protective strip now fractured from fatigue becomes a 
source of abrasion. There is a need for a better protective strip for 
extending the life of the flexible tubing. 
In order to change the delivery rate of the peristaltic pumps of the prior 
art, the diameter of the flexible conduit was changed as taught in the 
Gelfand patent. Changing the flexible conduit requires stopping the pump 
and substituting a different size conduit to change the delivery rate. The 
delivery rate could also be changed by varying the rotor speed, as is also 
taught in the Gelfand patent. The Berman et al U.S. Pat. No. 3,737,251 and 
Vial U.S. Pat. No. 3,990,444 show stepping motors being used to vary the 
rotor shaft speed. Stepping motors and other variable speed motors are 
expensive and eliminate the economic advantage that peristaltic pumps have 
over other pumps. Pumps such as piston pumps can easily change their 
delivery rate by merely varying the stroke of the piston. There is a need 
for a peristaltic pump having the capability of a variable delivery rate 
without the use of an expensive variable speed motor or the need of 
shutting down the pump and changing the flexible tubing. 
SUMMARY OF THE INVENTION 
The present invention is a variable volume peristaltic pump which can be 
driven by a single speed power source. The peristaltic pump has a housing 
with an arcuate chamber and a fixed length of flexible wall tubing 
arranged circumferentially in the arcuate chamber. An adjustable band is 
circumferentially arranged along the flexible conduit holding the conduit 
against the chamber wall. A plurality of rollers are rotatably attached to 
a rotor coaxially positioned within the arcuate chamber. The rollers 
engage the adjustable band and compress the flexible tubing against the 
wall of the arcuate chamber forcing fluid to flow through the flexible 
tubing. 
The adjustable band is secured to the housing at one end and is attached at 
the other end to adjusting means for varying the effective length of the 
adjustable band. When the effective length of the adjustable band is 
increased, the flexible tubing is flattened against the arcuate chamber 
wall, thereby changing the cross-sectional area of the tubing and 
consequently the volume. With the volume changed, the capacity of the 
flexible tubing has correspondingly been changed and the delivery rate of 
the pump altered. Retracting the adjustable band produces the opposite 
effect, allowing the tubing to increase its cross-sectional area thereby 
increasing the delivery rate of the pump.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 generally shows a peristaltic pump of the present invention with a 
housing generally indicated at 10. The pump housing 10 has an inlet 12 and 
an outlet 14. The pump housing 10 further has a base 16 and a center 
casing 18 with side wall panels 20 and 22 fixedly attached to each side of 
the center casing 18 by screw threaded fasteners 24. 
In FIGS. 2 and 3 a drive shaft 26 is shown rotatably attached to side walls 
20 and 22 and attached at end 28 to a motor (not shown). The drive shaft 
26 is mounted within a set of bearings 30 which are preferably mounted 
within side walls 20,22. The casing 18 and side walls 20,22 form an 
arcuate chamber 32, and the rotor 36 is situated coaxially within arcuate 
chamber 32. 
The rotor 36 is mounted on the drive shaft 26 and the rollers 34 are 
rotatably mounted by bearings 38 on shafts 40 which are fixedly attached 
at opposite ends of the rotor 36. Each roller 34 is rotatably attached 
between rotor arms 37. An O-ring 39 is situated within relief 41 and acts 
as a mechanical spring, absorbing variations in manufacturing tolerances 
within the arcuate chamber 32. 
A flexible conduit 44 having a fixed length is circumferentially spaced 
along the arcuate chamber wall 46. The flexible conduit 44 has an inlet 
opening 48 and an outlet opening 50 corresponding to the pump inlet 12 and 
outlet 14, respectively. The flexible conduit 44 transports the fluid 
being pumped through its interior. 
An adjustable band 52 is circumferentially positioned between the rollers 
34 and the flexible conduit 44. The adjustable band 52 holds the flexible 
conduit 44 against the chamber wall 46. The adjustable band 52 is 
pivotally attached to the pump housing 10 at one end 54 and is adjustably 
(and pivotally) attached to the pump housing 10 at the other end 56 as 
best seen in FIGS. 3 and 4. The end 54 is attached by a screw threaded 
fastener 58 to a trunnion 60 which is in turn mounted in the pump housing 
10. The screw threaded fastener 58 holds end 54 by engaging slot 62 and 
allows the end 54 to oscillate longitudinally within the slot 62 without 
any transverse movement resulting in minimization of the load on the 
trunnion 60 when the pump is in operation. 
The adjustable end 56 engages preferably a screw type adjusting clamp 64 
which includes an adjusting screw 66 and a body 68 having tabs (not shown) 
for keeping the adjusting screw 66 within the body 68. The clamp 64 is 
pivotally attached to the pump housing 10 and has a slot through which the 
adjustable end of the adjustable band 52 is received. A longitudinal 
section of the threads of adjusting screw 66 is received within the slot 
and engages grooves 70 of the adjustable end 56. When the adjusting screw 
66 is turned, the threads of the screw engage the grooves 70 and move the 
adjusting end 56 through the slot of the clamp 64, the direction depending 
on which way the adjusting screw 66 is turned, as indicated by an arrow 
71. The screw type clamp 64 has a similar mechanical movement to a 
conventional hose clamp used to secure rubber hoses in an automobile. It 
should be understood that any conventional means that securely holds the 
adjusting end 56 and has the capability of allowing infinitely variable 
adjustments during pump operation may be used without departing from the 
scope of the present invention. 
The adjustable band 52 is comprised of a stiffening band 52a and a 
strengthening band 52b. The stiffening band 52a is made of a polymer 
having sufficient fatigue resistance and a sufficient amount of 
flexibility, preferably polypropylene. A creep resistant strengthening 
band 53b is fixedly attached to the stiffening band 52a on the side 
engaging the flexible conduit 44 as shown in FIGS. 2 and 3. The 
strengthening band 52a is preferably made of beryllium copper alloys, 
beryllium nickel alloys or 400 series stainless steel alloys. However, any 
material having adequate fatigue resistance will suffice. Materials 
commonly used for coiled and flat springs are most applicable because they 
have a high endurance limit when compared to other materials. But 
resiliency is not required of metal band 52b. Its purpose is to prevent 
stretching ("creep" due to tensile forces) of the plastic band 52a and 
provide strong attachments with the worm screw 66 and the pivoting arm at 
second pivot point 76. "Creep" is defined as permanent deformation due to 
an inability of a stressed member to completely recover its original 
shape. For example, if plastic is stressed for a prolonged period, 
molecular bonds will dislocate within the microstructure of the material, 
causing permanent deformation. Creep in metals is negligible at normal 
levels of stress. Creep in plastics is a common problem and occurs at very 
low stress levels. 
The basic purpose of the composite band 52 formed by plastic band 52a and 
metal band 52b is to maintain an essentially circular spiral during pump 
operation. It must have a stiffness that provides a gradual curvature 
within the circumstance of the chamber, thus avoiding excessive contact 
forces and highly localized tubing stresses. For a given pump geometry and 
a given tubing diameter, the band length and required deflection is 
defined; and tubing stiffness determines the minimal band rigidity that is 
desirable. Given a fixed length and a required deflection, the band 
stiffness is essentially a function of only two variables--the elastic 
modulus (a material property) and the section modulus (a geometric 
property of the cross section). Band stiffness is proportional to the 
product of these elements. A metal band could be constructed with the 
proper stiffness. However, for practical limitations of pump geometry and 
tubing products, the induced bending stresses exceed the endurance limit 
of all practical metal alternatives. Hence, the preferred embodiment of 
the present invention uses a composite, laminated band construction formed 
by bands 52a and 52b. 
The relatively thick plastic band 52a provides a large section modulus. The 
low elastic modulus common to plastic materials minimizes internal 
stresses during flexure and polypropylene is particularly advantageous 
because of its exceptional fatigue strength. The polypropylene band 52a 
provides the necessary flexural characteristics of stiffness and fatigue 
life but lacks the necessary tensile requirements of strength and creep 
resistance. The metal band 52b provides those needs. The stiffness of the 
plastic band 52a keeps the radius of curvature of the composite band large 
during flexure. Because the radius of flexure is large and the thickness 
of the metal band 52b is small, internal stresses in the metal component 
are effectively kept below the material endurance limit. At the same time, 
sufficient tensile strength is available for the attachments at points 56 
and 76. The plastic and metal bands 52a and 52b reinforce each other while 
together fulfilling the mechanical demands of pump operation. 
As shown in FIG. 2 the flexible conduit 44 is situated between the arcuate 
chamber wall 46 and the strengthening band 52b, being held in place by 
retaining members 75. The spacing between the retaining members 75 is 
sufficient to accept several tubing sizes. The retaining members 75 and 
the thickness of the plastic band 52a provide a gradual curvature of the 
adjustable band 52 within the arcuate chamber thereby avoiding any high 
localized stress to the flexible conduit. 
A pivoting arm 72 is pivotally attached to the pump housing 18 at first 
pivot point 74 at one end and to the adjustable band 52 at second pivot 
point 76 at the other end. The second pivot point 76 is located directly 
below the center of the drive shaft 26, and first pivot point 74 is 
located on the side of the pump housing 10 which is toward the direction 
of rotation 42 of the rotor 36 as shown in FIG. 3. The pivoting arm 72 
keeps the flexible band 52 substantially centered within the arcuate 
chamber 32. 
Several advantages and effects are realized in the combination of the 
pivoting arm 72 and the manner that the screw threaded fastener 58 holds 
end 54 to the trunnion 60. First, any net tensile or compressive forces 
are avoided in the discharge half of the adjustable band 52, defined from 
the second pivot point 76 to end 54. Secondly, the suction half of the 
adjustable band, defined from adjustable end 56 to second pivot point 76, 
is always in a net positive tensile posture, ensuring that buckling of the 
adjustable band will not occur. The net positive tensile force in the 
adjustment band will also cause the band to be forced away from the 
flexible conduit. Thirdly, any net tensile force in the pivoting arm 72 
will always be positive, avoiding any buckling of the pivot arm. Fourthly, 
the pivoting arm 72 effectively contains the adjustment of the adjustable 
band to the suction side of the pump between the adjusting clamp 64 and 
the second pivot point 76. The function of the discharge portion of the 
adjustable band is only to provide a continuous roller contact, thereby 
maintaining a positive seal for an entire revolution of the rollers 34. 
Lastly, any variations in manufacturing tolerances are easily absorbed by 
the pivoting arm 72 and the manner of attachment of the end 54 to the 
trunnion 60. 
The adjustable band 52 serves several purposes. The adjustable band 52 
protects flexible conduit 44 from the direct contact of the rollers 34 
thus avoiding abrasion, and the abrupt and highly localized tensile and 
shear stresses otherwise caused by direct contact with the rollers and 
extending the life of the flexible conduit 44. The retaining members 75 of 
the flexible conduit 44 aid in extending the life of flexible conduit 44 
by retaining the flexible conduit 44 within the protection of the 
adjustable band 52. In addition, retaining members 75 prevent any twisting 
of the flexible conduit 44 which would otherwise occur if the flexible 
conduit 44 was allowed movement in the axial direction. The preferred 
combination of the metal band 52b and the polypropylene band 52a add to 
the life of the adjustable band 52 while also providing a sufficient 
buffer for protecting the flexible conduit 44 from undue flexing and 
abrasion caused by the continuous action of the rollers 34. 
The inherent spring-back characteristic of round resilient tubing is relied 
upon in prior art peristaltic pumps to draw fluid into the pump and to 
provide a consistent volumetric displacement. The stronger the 
spring-back, the higher the suction draw and also the more consistent the 
delivery rate. However, the induced stresses that provide spring-back in 
round tubing are essentially the same ones causing tubing failure. The 
present invention accommodates the same resilient tubing used in prior art 
peristaltic pumps, but does not have to rely on inherent spring-back 
characteristics to the same extent. The adjustable band 52 and the casing 
bore combine to provide effective control of tubing recovery, and reduce 
the need for round tubing. 
A round conduit is not necessary fo consistent delivery and therefore high 
stress levels can be avoided. In such cases, fluid can be induced into the 
pump either mechanically (e.g. physical attachment of the conduit to its 
radial boundaries), or hydraulically (e.g. a positive suction pressure). 
The detrimental levels of tubing stress that accompany the utilization of 
spring-back in prior art peristaltic pumps can be avoided with the present 
invention. 
The adjustability of the adjustable band 52 provides the present invention 
with the capability of a variable delivery rate without replacing conduit 
44 and without the need of an expensive speed motor. With the present 
invention, the delivery rate can be changed while the peristaltic pump is 
operating. FIG. 5 shows a calibration curve of one model of the 
peristaltic pump of the present invention that has a round flexible 
conduit with a one-quarter inch inner diameter and an arcuate chamber 
having a five inch bore diameter. The peristaltic pump was operated at 
89.3 revolutions per minute. The horizontal axis entitled "Turns 
Adjustment" refers to the number of turns that the adjusting screw 66 was 
turned from a zero point. The vertical axis entitled "Delivery rate, cubic 
centimeters per minute" refers to the output of the particular model of 
the peristaltic pump of the present invention. At the zero point, the 
delivery rate is zero and the adjusting screw is at a point where the 
flexible conduit is completely flattened against the chamber wall by the 
adjustable band, the adjustable band being at the longest length possible 
within the arcuate chamber. Turning the adjusting screw shortens the 
flexible band 52, removing pressure from the flexible conduit 44 and 
increasing the volumetric capacity of conduit 44. This results in an 
increased delivery rate of the peristaltic pump as shown by the data 
points in the calibration curve connected by lines. 
The capability of varying the delivery rate while the peristaltic pump is 
operating eliminates the need for a costly variable speed motor. Further 
economies can be achieved by driving several pumps with the same constant 
speed motor, each pump having the capability of being adjusted 
independently during operation. Also, several pumps can be driven by the 
same single speed motor, each pump having a flexible conduit with a 
different inner diameter providing a wide array of delivery rates, all 
delivery rates being adjustable during operation. 
Although the present invention has been described with reference to 
preferred embodiments, workers skilled in the art will recognize that 
changes may be made in form and detail without departing from the spirit 
and scope of the invention.