WO2004106742A1

WO2004106742A1 - Rotary piston pump with pressure relief

Info

Publication number: WO2004106742A1
Application number: PCT/US2003/016858
Authority: WO
Inventors: Duane Ehlke
Original assignee: Fristam Pumps, Inc.
Priority date: 2003-05-29
Filing date: 2003-05-29
Publication date: 2004-12-09
Also published as: AU2003238781A1

Abstract

A rotary piston pump (100) includes a pump housing (102) having an interior housing wall (104) at least partially surrounding a pump interior (106), with the interior housing wall opening at a pump inlet (108) at the low-pressure side of the pump and a pump outlet (110) at the high-pressure side of the pump. Rotors (112) bearing radially protruding pistons (114) are situated with the pump interior, and the pistons intermesh between the pump inlet and the pump outlet. A movable relief member (122) such as a piston is situated on a portion of the interior housing wall, and may move toward or away from the pump interior to alter the effective volume of the pump interior and alter the pressure therein. The relief member is preferably resiliently and elastically biased toward the pump interior, as by a spring (140), whereby the relief member will yield and move away from the pump interior when excess pressure conditions exist therein. The relief member is preferably situated between the pump inlet and the pump outlet adjacent the region where the pistons intermesh so that retraction of the relief member will effectively define a passage between the low-pressure side of the pump and the high-pressure side of the pump, thereby allowing at least partial equalization of the pressure therebetween when the pressure difference between the sides reaches an excessive level.

Description

ROTARY PISTON PUMP WITH PRESSURE RELIEF

Inventors: Duane Ehlke

Field of the Invention This document concerns an invention relating generally to rotary piston pumps , and more specifically to rotary piston pumps which include means for relieving potentially damaging excess pressure within the pumps.

Background of the Invention Rotary piston pumps are positive displacement pumps useful for pumping fluid materials, particularly viscous fluid materials such as slurries. As illustrated in prior patents, such as (for example) U.S. Patent 1,702,046 to Fullertoir, U.S. Patent 3,817,667 to Winkelstrater et al ; U.S. Patent 4,453,901 to Zimmerly et al. ; and U.S. Patent 5,336,069 to Matsuyama, such pumps generally use at least a pair of rotors which rotate within a pump housing, with the rotors bearing pistons which intermesh between a pump inlet (a low-pressure side) and a pump outlet (a high- pressure side). Such pumps may be considered to include gear pumps (as shown, for example, in U.S. Patent 5,190,450 to Ghosh et at), and pumps of the intermeshing vane type (as shown, for example, in U.S. Patent 4,057,375 to Nachtrieb). As noted in prior patents owned by the Applicant or Assignee noted on this document (e.g., UK Patent Appln. GB 2294728A, as well as its equivalents DE 4437178 and JP 8210262), rotary piston pumps can be damaged if an extreme pressure difference arises between the low-pressure inlet side and the high-pressure outlet side, in which case the pistons may begin to bend with respect to their rotors. The seal between the rotors may then be lost, leading to pumping inefficiencies, and additionally the pistons may grind against each other and/or against the pump housing. In the past, this problem has been addressed by providing a relief conduit which extends outside the pump housing from the high-pressure outlet side to the low- pressure inlet side, and wherein a normally-closed relief valve is provided in the relief conduit. Thus, when the pressure difference between the high-pressure outlet side and the low-pressure inlet side grows too extreme, the relief valve opens and the pumped fluid is at least partially diverted through the relief conduit to flow from the outlet side to the inlet side, which serves to reduce the pressure difference therebetween. Since the fluid being pumped is often quite viscous, and may include mixtures of solids and liquids, the structure of the relief valve is preferably made as simple as possible to diminish the possibility of clogging and to ease maintenance and repair. A commonly used structure for the relief valve is an elastomeric diaphragm affixed to a plate in face-to-face abutment, with the relief conduit extending from the high-pressure outlet side, between the diaphragm and plate (which are in abutment, thereby effectively closing the conduit), and to the low-pressure inlet side. When the pressure difference between the outlet side and the inlet side exceeds some threshold level, the diaphragm will yield and provide a path between the diaphragm and plate, thereby allowing fluid to flow through the relief conduit from the high-pressure outlet side to the low- pressure inlet side. When the pressure difference decreases, the diaphragm retracts to its non-distended state and closes the relief conduit.

However, the foregoing pressure relief arrangement does not work well where the pump is to be used in food processing and other sanitary applications where the pump must be cleaned regularly. The fluid being pumped accumulates in the relief conduit, as well as in the relief valve itself, and is difficult to dislodge because standard clean-in-place procedures will not fully clean the various crevices presented by the arrangement, As a result, the foregoing arrangement is effectively unusable in sanitary applications. Even if it was decided to implement the arrangement in conjunction with the use of a highly rigorous cleaning methodology (e.g., partial disassembly of the arrangement accompanied by steam flushing), the increase in cleaning time - which represents a loss of production time during the period when the pump is taken from service - would be so great as to be infeasible. Summary of the Invention

The invention involves a rotary piston pump which is intended to at least partially solve the aforementioned problems. A brief summary of preferred versions of the rotary piston pump follows to give the reader a basic understanding of some of their advantageous features. As this is merely a summary, it should be understood that more details regarding the preferred versions may be found in the Detailed Description set forth elsewhere in this document. The claims set forth at the end of this document then define the various versions of the rotary piston pump in which exclusive rights are secured. Preferred versions of the rotary piston pump include a pump housing having an interior housing wall at least partially surrounding a pump interior, with the interior housing wall opening at a pump inlet and a pump outlet. Rotors are situated within the pump interior, and the rotors bear radially protruding pistons which intermesh between the pump inlet and the pump outlet so that as the rotors rotate, the pistons of one rotor move between the pistons of another rotor. When fluid material is provided to the pump inlet, such motion of the pistons forces the fluid material through the pump interior to the pump outlet, with the pump interior adjacent the pump inlet thereby defining the low-pressure side of the pump and the pump interior adjacent the pump outlet thereby defining the high-pressure side of the pump. Since a pump of this nature is susceptible to wear and damage if the pressure within the pump interior is too great - more particularly, if the pressure difference between the low-pressure side and high-pressure side is too great - a means for relieving the pressure within the pump interior is provided. Such pressure relief means preferably takes the form of a relief member which defines a portion of the interior housing wall, and which is movable within the pump housing adjacent the pump interior, whereby moving the relief member toward or away from the pump interior will alter the volume of the pump interior. The relief member may simply take the form of a piston translating in a bore defined in the pump housing, with the relief member having an interior face at the pump interior. The relief member is preferably resiliently and elastically biased toward the pump interior, as by a spring, whereby the relief member will yield and move away from the pump interior when excess pressure conditions exist therein. Thus, the relief member may move so that its interior face travels away from the pump interior to increase the volume of the pump interior, and thereby reduce the pressure therein. Alternatively, the relief member may move so that its interior face travels back toward the pump interior, thereby increasing pressure or restoring it to its standard operating state. The spring or other means for elastically biasing the relief member preferably has adjustable tension, as by situating the elastic biasing means between the relief member and a tensioning member which has adjustable spacing with respect to the relief member.

Thus, the tensioning member may be moved towards the relief member to increase spring force and thereby increase the pressure threshold at which the relief member will begin to yield and move away from the pump interior, or may be moved away from the relief member to decrease spring force and thereby reduce the pressure threshold.

Most preferably, the relief member is situated between the pump inlet and the pump outlet, more specifically between the axes about which the rotors rotate and adjacent the region where the pistons intermesh. This location situates the relief member directly between the low-pressure side and high-pressure side of the pump interior, whereby the relief member may move away from the pump interior to allow fluid material to bleed between the low-pressure side and high-pressure side if the pressure difference between them grows too great, The interior face of the relief member may be elongated, with its length extending between the pump inlet and the pump outlet, to better define a passage between the low-pressure side and high- pressure side when the relief member moves away from the pump interior.

For sanitary purposes, it is useful to interpose a seal between the relief member and the pump housing, and also between the relief member and the pistons, to prevent the fluid material being pumped from creeping into the bore between the relief member and the pump housing. This enhances the ability of the pump to be thoroughly cleaned in place, as by flushing it with cleaning liquids, so that all of the fluid material is removed when flushing occurs.

Further advantages, features, and objects of the invention will be apparent from the following detailed description of the invention in conjunction with the associated drawings.

Brief Description of the Drawings

ETG. 1 is a side elevational view of a cross-section of a rotary piston pump

100 exemplifying the invention, with a left side of the pump housing 102 being shown, but with the right side omitted, and with the relief member 122 being shown in an extended state characteristic of standard (non-excessive) pump operating pressures.

ETG. 2 is a side elevational view of the rotary piston pump 100 of ETG. 1 shown with the relief member 122 in a partially retracted state characteristic of excessive pump operating pressures.

ETG. 3 is a front elevational view of the rotary piston pump 100 of ETGS. 1 and 2, showing the exterior of the pump housing 102 and the head 146 of the tensioning member 142 used to adjust the pressure at which the relief member 122 will be triggered. ETG. 4 is a rear elevational view of the pump 100 of ETGS. 1-3 showing the rotors 112 and pistons 114 of the pump 100 in conjunction with the relief member 122.

Detailed Description of Preferred Versions of the Invention In the drawings, wherein the same or similar features of the invention are designated in all Figures with the same reference numerals, a rotary piston pump exemplifying the invention is depicted generally by the reference numeral 100. The rotary piston pump 100 includes a pump housing 102, and throughout the drawings, the pump housing 102 is only partially depicted (with its front half being shown) . The pump housing 102 has an interior housing wall 104 which surrounds a pump interior 106 wherein the fluid material being pumped travels. The interior housing wall 104 opens at a pump inlet and a pump outlet, which are not directly depicted in the drawings because they are provided in the omitted rear half of the pump housing 102; however, the general location of an exemplary pump inlet 108 and a pump outlet 110 are shown projected on the front half of the pump housing 102 in phantom lines in ETG. 4.

Referring particularly to ETGS. 1-2 and 4, a pair of rotors 112 are situated within the pump interior 106, and the rotors 112 each have radially extending pistons 114 which orbit their rotors 112 within the pump interior 106. The pistons 114 of each rotor 112 rotate between the pistons 114 of the other rotor 112 at an intermeshing region 116 of the pump interior 106 located between the pump inlet 108 and pump outlet 110, and between the axes about which the rotors 112 rotate. Thus, when fluid material is provided to the pump inlet 108, the rotation of the rotors 112 and their pistons 114 forces the fluid material through the pump interior 106 to the pump outlet

108. The pump interior 106 adjacent the pump inlet 108 therefore defines a low- pressure pump side 118 (see ETG. 4), whereas the pump interior 106 adjacent the pump outlet 110 defines a high-pressure pump side 120.

To relieve excessive pressure within the pump interior 106, a relief member 122 may be provided on the interior housing wall 104, with the relief member 122 being movable within the pump housing 102 toward or away from the pump interior 106. As a result, moving the relief member 122 alters the effective volume of the pump interior 106, thereby allowing pressure to be relieved if the relief member 122 is retracted to expand the effective volume of the pump interior 106 (as in ETG. 2), or increased if the relief member 122 is extended to decrease the effective volume of the pump interior 106 (as in FIG. 1). The relief member 122 is depicted as a piston which travels within a bore 124 in the pump housing 102, with the relief member 122 having an interior face 126 at the pump interior 106 adjacent the intermeshing region 116, and between the pump inlet 108 aqd pump outlet 110. While this is the preferred location for the relief member 122 for reasons to be discussed below, the relief member may be situated elsewhere on the interior housing wall 104, e.g. , on the high- pressure pump side 120 adjacent the pump outlet 110.

While motion of the relief member 122 might be mechanically, pneumatically, or otherwise actuated in response to the monitored pressure within the pump interior

106, a preferred arrangement is to resiliently and elastically bias the relief member 122 towards the pump interior 106, as by using arrangements to be discussed below, whereby the relief member 122 will automatically yield and move out of the pump interior 106 when the pressure therein exceeds some threshold value. Thus, if the pressure threshold is exceeded, the interior face 126 of the relief member 122 will automatically retreat from the pump interior 106 as depicted in ETG.2 to increase the effective volume of the pump interior 106, thereby reducing the pressure therein. When the pressure within the pump interior 106 returns to standard values - in other words, when the pressure drops below the pressure threshold - the relief member 122 can automatically move to situate its interior face 126 at its standard non-actuated position (as depicted in ETG. 1), thereby maintaining the cunent pressure state within the pump interior 106 until the pressure threshold is again exceeded.

The relief member 122 is preferably provided with tensioning means for adjustably altering the threshold pressure at which the relief member 122 will begin to yield, and a preferced arangement is as follows. Referring to FIGS, 1 and 2, the relief member 122 has an exterior face 128 opposite its interior face 126, and the exterior face 128 is affixed to a seating cap 130 via a fastener 132. The seating cap 130 travels within a bore 134 defined within a casing 136, with the casing preferably being removably affixed to the pump housing 102 by fasteners 138 for ease of maintenance. The diameter of the seating cap 130 is greater than the diameter of the bore 124 wherein the relief member 122 travels, and thus the seating cap. 130 limits the extent of travel of the relief member 122 inwardly towards the pump interior 106, so that the interior face 126 of the relief member 122 is ordinarily situated just outside the orbit of the pistons 114 at the intermeshing region 116. A spring 140 extends between the seating cap 130 and an adjustable tensioning member 142 which allows adjustment of the tension of the spring 140. The tensioning member 142 may take the form of a screw having a threaded end 144 engaging the casing 136 and bearing against the spring 140, and a head 146 which may be actuated to adjustably space the tensioning member 142 from the seating cap 130 (and thus from the relief member

122). Thus, by moving the tensioning member 142 towards the relief member 122, the force of the spring 140 on the seating cap 130 (and relief member 122) is increased, thereby increasing the pressure threshold at which the relief member 122 will begin to yield and move away from the pump interior 106. Conversely, by moving the tensioning member 142 away from the seating cap 130 (and the relief member 122), the force of the spring 140 will be decreased, and the pressure threshold at which the relief member 122 will yield will likewise be decreased.

As noted previously, the relief member 122 is preferably located with its interior face 126 adjacent the intermeshing region 116, and between the pump inlet 108 and pump outlet 110. As best seen in ETG. 4, a particularly preferred arrangement is to provide the relief member 122 with an elongated interior face 126, having its length extending between the low-pressure pump side 118 and the high- pressure pump side 120, to better define a passage therebetween when the pressure threshold is exceeded and the relief member 122 moves away from the pump interior 106, As a result, the space evacuated by the relief member 122 provides a passage between the low-pressure pump side 118 and the high-pressure pump side 120, allowing fluid material to bleed between the two sides to relieve excess pressure.

When the rotary piston pump 100 is to be used in food processing and other sanitary applications, it is useful to interpose one or more seals 148 between the relief member 122 and the pump housing 102, such as an elastomeric O-ring or O-rings, whereby any fluid material being pumped is prevented from creeping into the bore 124 between the relief member 122 and the pump housing 102, Thus, when the pump 100 is cleaned - as by pumping flushing liquid between the pump inlet 108 and pump outlet 110 - the interior face 126 of the relief member 122 will be cleaned along with the remainder of the pump interior 108, and no passages or other crevices will be left wherein leftover material can accumulate.

It should be understood that the foregoing drawings and description merely review aprefened version of the invention, and the invention encompasses numerous variations from the prefened version. As a first example, while the spring 140 is depicted as a helical spring, other types of springs may be accommodated instead of (or in addition to) helical springs, such as springs formed of elastomeric members, pneumatic springs, or other structures providing a resilient biasing force.

As a second example, while the preferred relief member 122 was described as being located between the high-pressure pump side 120 and the low-pressure pump side 118 adjacent the intermeshing region 116 wherein the pistons 114 commingle, as noted above, the relief member 122 may be situated elsewhere (e.g., solely on the high-pressure pump side 120, though such an arrangement would achieve a more limited degree of pressure relief). It is also possible to provide multiple pressure relief members 122 within the same pump 100, as by including two relief members

122 as depicted, but each being situated on opposing sides of the pump housing 102, and/or by situating one or more relief members 122 between the high-pressure pump side 120 and the low-pressure pump side 118 and one or more relief members 122 elsewhere (e.g., solely on the high-pressure pump side 120). As another example, while the preferred relief member 122 is depicted as having an elongated interior face 126 so that retreat of the relief member 122 from the pump interior 106 will effectively define a pressure-relieving passage between the pump inlet 108 and the pump outlet 110, the relief member may take other forms to define paths from one region within the pump interior 106 to another as desired, or may simply take a form wherein some limited region of the pump interior 106 - e.g., the high-pressure side - may have its volume effectively expanded by retraction of the relief member 122 when the pressure therein grows too great.

The invention is not intended to be limited to the preferred versions of the invention described above, but rather is intended to be limited only by the claims set out below. Thus, the invention encompasses all different versions that fall literally or equivalently within the scope of these claims.

Claims

ClaimsWhat is claimed is:

1. A rotary piston pump comprising: a. a pump housing having a pump inlet, a pump outlet, and an interior housing wall at least partially surrounding a pump interior, b. a relief member movable in the pump housing adjacent the pump interior, whereby motion of the relief member alters the volume of the pump interior; and c. rotors situated within the pump interior, the rotors having protruding intermeshing pistons.

2. The rotary piston pump of claim 1 wherein the relief member is situated between the pump inlet and the pump outlet.

3. The rotary piston pump of claim 2 wherein the pistons intermesh between the pump inlet and the pump outlet.

4. The rotary piston pump of claim 1 wherein the relief member is located immediately adjacent the area at which the pistons intermesh,

5. The rotary piston pump of claim 1 wherein the rotors each rotate about a rotor axis, and wherein the relief member is situated between the rotor axes.

6. The rotary piston pump of claim 1 wherein the relief member defines a piston movable in the pump housing, the relief member having an interior face at the pump interior.

7. The rotary piston pump of claim 6 wherein the interior face of the relief member is elongated, with its length extending between the pump inlet and the pump outlet.

8. The rotary piston pump of claim 1 further comprising a removable seal situated between the relief member and the pump housing.

9. The rotary piston pump of claim 1 wherein the relief member is resiliently biased toward the pump interior.

10. The rotary piston pump of claim 1 wherein the relief member includes: a. an interior face at the pump interior, and b. an opposing exterior face biased by a spring.

11. The rotary piston pump of claim 10 wherein the spring is situated between the exterior face of the relief member and a tensioning member, and wherein the tensioning member is adjustably movable to adjust the biasing of the spring with respect to the exterior face of the relief member.

12. A rotary piston pump comprising: a. a pump housing having an interior housing wall opening at a pump inlet and a pump outlet, b. rotors bearing extending pistons, wherein the rotors rotate to move the pistons of one rotor between the pistons of another rotor between the pump inlet and the pump outlet; c. a relief member on the interior housing wall between the pump inlet and the pump outlet, the relief member being movable within the pump housing,

13. The rotary piston pump of claim 12 wherein the rotors each rotate about a rotor axis, and wherein the relief member is situated between the rotor axes.

14. The rotary piston pump of claim 12 wherein the relief member is situated on the interior housing wall immediately adjacent the region wherein the pistons of one rotor move between the pistons of another rotor.

15. The rotary piston pump of claim 12 wherein the relief member has an interior face: a. adjacent at least one of the rotors; and b. being movable toward and away from the rotors.

16. The rotary piston pump of claim 15 wherein the interior face of the relief member is adjacent two rotors at the region wherein the pistons of one rotor move between the pistons of another rotor.

17. The rotary piston pump of claim 15 wherein the interior face of the relief member is elongated in a direction extending between the pump inlet and the pump outlet.

18. The rotary piston pump of claim 12 further comprising a removable seal situated between the relief member and the pump housing,

19. The rotary piston pump of claim 12 wherein the relief member is elastically biased toward the rotors.

20. The rotary piston pump of claim 12 wherein the relief member includes: a. an interior face adjacent one or more of the rotors, and b. an exterior face which is elastically biased to urge the interior face towards the one or more rotors.

21. The rotary piston pump of claim 12 further comprising: a. a tensioning member adjustably movable with respect to the pump housing; and b . a spring situated between the relief member and a tensioning member, the spring elastically biasing the relief member toward the rotors, wherein movement of the tensioning member adjusts the biasing of the spring with respect to the relief member.

22. A rotary piston pump comprising: a. a pump housing having an interior housing wall extending about a pump interior, with the pump interior opening onto a pump inlet and a pump outlet; b. adjacent rotors within the pump interior, the rotors bearing radially extending pistons which intermesh between the pump inlet and the pump outlet; c. a relief member defining a portion of the interior housing wall, the relief member being movable within the pump housing whereby moving the relief member varies the volume of the pump interior,

23. The rotary piston pump of claim 22 wherein the relief member is situated between the pump inlet and the pump outlet.

24, The rotary piston pump of claim 23 wherein the relief member is immediately adjacent to the intermeshing pistons,

25. The rotary piston pump of claim 24 wherein the relief member moves within the pump housing toward and away from the intermeshing pistons.

26. The rotary piston pump of claim 22 wherein the relief member is a piston having an elongated interior face, with the length of the interior face extending between the pump inlet and the pump outlet.

27. The rotary piston pump of claim 22 wherein the relief member is a piston movable within the pump housing, and wherein a removable seal is situated between the relief member and the pump housing.

28. The rotary piston pump of claim 22 further comprising a replaceable seal interposed between the relief member and the pump housing.