US3551067A

US3551067A - Lined corrosion resistant pump

Info

Publication number: US3551067A
Application number: US792938*A
Authority: US
Inventors: Jack L Wissman
Original assignee: Duriron Co Inc
Current assignee: Flowserve Corp
Priority date: 1969-01-22
Filing date: 1969-01-22
Publication date: 1970-12-29
Anticipated expiration: 1987-12-29
Also published as: CH521523A; DE2001267C3; BE744777A; ES375416A1; NL7000935A; FR2028910A1; DE2001267A1; JPS4947323B1; AT306524B; GB1296964A; DE2001267B2

Description

LINED CORROSI Filed Jan. 22, 1969 J. L'. wlsswm ON RESISTANT PUMP 3 Sheets-Sheet 1 INVENTOI? JACK L. WISSMAN ATTORNEYS Dec. 29, 1970 J w 5 I 3,551,067

LINED CORROSION RESISTANT PUMP Filed Jan. 22, 1969 5 Sheets-Sheet 2 nos F G 6 m8 :Inu

Dec. 29, 1970 w 55 LINED CORROSION RESISTANT PUMP Filed Jan. 22, 1969 5 Sheets-Sheet 3 FIG-9 United States Patent O York Filed Jan. 22, 1969, Ser. No. 792,938 Int. Cl. F01d 1/02, 9/00, 25/26 US. Cl. 415-134 14 Claims ABSTRACT OF THE DISCLOSURE A pump includes a casing and cover assembly forming a chamber having an inlet and an outlet. The fluid contacted surfaces of the casing and cover assembly are sheathed with polytetrafluoroethylene, the sheaths including neck portions extending through the inlet and outlet and being flanged for mounting conduits in the usual way. A driven impeller is positioned within the chamber, and all fluid contacted surfaces of the impeller are covered with polytetrafiuoroethylene. The sheaths include peripheral portions clamped between the casing and cover assembly to provide a seal therebetween, these peripheral portions being secured against movement radially inwardly. The inner periphery of the sheath covering the cover is also secured against radially inward movement.

BACKGROUND OF THE INVENTION The present invention relates to pumps and more particularly to an improved centrifugal pump for use with corrosive materials wherein the pump chamber is fully sheathed with polytetrafluoroethylene, and wherein the impeller is a corrosion resistant material or is also covered with corrosion resistant coating of polytetrafluoroethylene.

It is known to form pump parts of solid or filled polytetrafluoroethylene (PTFE), see for example US. Pat. No. 2,880,676 of April 1959 and U.S. Pat. No. 2,966,860 of January 1961.

It is also known to use a copolymer of a fluorocarbon resin to form a lining on a pump chamber. In the latter structure, the internal surfaces of the chamber include anchoring or locking apertures which receive locking lugs on the outside surface of the liner, the liner being of material such as fluorinated ethylene propylene. The purpose of the locking lugs and apertures is to prevent movement of the liner in response to increases in temperature. PTFE being more like a thermosetting resin as opposed to the fluorinated copolymers which are thermoplastic, does not require locking lugs or apertures to maintain a stable configuation over a range of temperatures, e.g., F. to +400 F.

The processing of fluorinated copolymers is quite different from that used with PTFE in that the latter has a plastic memory which tends to cause the part to revert to is originally formed shape when heated in an unconfined condition. For example, a part of PTFE which has been sintered can be hot or cold worked to change its shape, but once heated in an unconfined state, the part tends to revert to its original sintered shape. If unconfined and heated to the range of 700 to 750 F., a hot or cold worked part will revert to its sintered configuration. In its original sintered form the part has a primary memory of that shape, and once worked, the part has a secondary memory of its worked shape. Thermoplastics do not have both a primary and secondary memory as does PTFE. The secondary memory may create difliculty because temperature cycling can cause sufficiently serious distortion of the part to render it useless for its designed purpose.

In pumps used in the chemical process industry there are several general factors which are usually considered in the design of a pump, as follows: (1) pump parts, espe 3,551,067 Patented Dec. 29, 1970 "ice cially the wet end must be of corrosion resistant alloys, (2) mechanical design must take into account the physical characteristics of the alloy (3) the wet end should be interchangeable so that dilferent wet ends may be used with different chemicals and (4) the pump should be eflicient in its operation.

The corrosion encountered in the pumps in the chemi cal processing industry may be of various types, such as:

(a) Chemical corrosion, i.e., nitric acid on bronze or hot sulfuric acid on Type 304 steel;

(b) Pittingbelieved to be failure of alloy to form the resistant oxide film;

(c) Galvanicuse of dissimilar materials and electro chemical corrosion of the part which is the anode;

(d) Concentration corrosion-local corrosion where small pockets of liquid are trapped;

(e) Erosionmechanical destruction by high velocity materials or slurry;

(f) Fatigue corrosion-a combination of the above;

(g) Dezincificationzinc is leached from the alloy and deposited back electrolytically; and

(h) Intergranular corrosionthe formation of chro mium carbide around a portion of the grains in stainless steels.

Apart from the question of corrosion resistance, there are several other factors which are considered in the design of a pump, such as:

(a) The pump should not act as a source of contamination for the fluid being pumped, e.g., pumps for use in the food and beverage field, the pharmaceutical industry and certain types of service in the chemical process industry;

(b) Non-adherent wet ends, i.e., the wet end is designed so that the material pumped does not adhere thereto; and

(c) Non-sparking due to metal-to-rnetal contact of parts in the wet end of the pump.

The design of pumps and interchangeability of wet end parts has been an important factor because of the variety of services in the chemical processing industries and the recognition that some of the alloys do not lend themselves to certain designs or service. Other factors are the performance of the pump, usually expressed in various ways, for example, gallons pumped per minute, total head in feet, net positive suction head, etc. It is a real advantage to be able to provide a pump usable for different types of services so as to eliminate the need for interchangeable wet ends. Where such a pump can be provided by utilizing the easy to machine alloys which provide good mechanical strength, an additional practical advantage exists. As a general rule, the corrosion resistant alloys customarily used are either diflicult to machine or diflicult to cast. A corrosion resistant pump of easily cast and machined alloys which maintains good operating parameters, especially one capable of being used with several different types of chemicals offers a real practical advantage by avoiding a substantial number of problems.

SUMMARY OF THE INVENTION In accordance with the present invention, a pump of the centrifugal type is provided in which all fluid contacted surfaces of the pump chamber are coated with a relatively thin coating or liner of PTFE, the liner being sufliciently thick to prevent passage of corrosive materials therethrough while being sufficiently thin to be characterized as a coating orliner. The chamber is formed by a casing and cover assembly each sheathed with a liner of PTFE, the liner also acting as a seal between these parts. The chamber is provided with an inlet and an outlet, also sheathed in PTFE, each of the inlet and outlet passages including a flange of PTFE which is integral with the associated sheath or liner thereby forming a seal with the attached piping.

Received within the chamber is an impeller which is also corrosion resistant, i.e., sheathed or lined with PTFE to form an encapsulated impeller, or of a corrosion resistant metal such as titanium, zirconium, or epoxy resin and the like. The impeller is driven by a shaft which preferably includes a PTFE sleeve thereon, and in the case of an encapsulated impeller, integrally formed with the coating of the impeller proper, a seal being provided between the cover and the shaft. The sheaths on the casing or cover assembly include peripheral portions in facing sealed relationship, and means are provided to secure these peripheral portions of the sheaths against radially inward movement in response to temperature cycling or relief of residual stresses in this part of the sheaths. The sheath which covers the casing also includes an inner peripheral portion securely anchored against radially inward movement. Because the sheaths are originally formed and sintered in a configuration generally corresponding to the configuration of the part with which they are associated, and since the sheaths are securely anchored relative to the parts to which they are associated, the sheaths remain in a stable configuration over a wide temperature range.

One of the features of the present invention is the provision of a sheath or liner of corrosion resistant substantially chemically inert plastic material which possesses exceptional temperature stability over a wide range of temperatures, e.g., 20 to +400 F. This is achieved by forming a sheath of PTFE so that the major portions thereof are formed in a configuration essentially that of its final configuration. Specifically, the portions of the sheath which are contacted by fluid are formed and sintered in a configuration corresponding essentially to that which the part has in the assembled pump. Since PTFE has a primary memory which is stable over the entire useful temperature range of the part, there is little tendency for the portion contacted by fluids to change shape. In other words, the portions of the sheaths contacted by fluid behave like a thermosetting resin to the extent that they possess a primary memory of their sintered and assembled configuration. Since the portions of the sheath which come in contact with fluid are not hot or cold worked they do not have a secondary memory of a shape different from that in which they were formed.

There are portions of the sheaths which do have a secondary memory, i.e., the peripheral portions, and these are clamped in place so that movement thereof is substantially eliminated, as previously noted.

Self-priming centrifugal pumps may also be fully sheathed to provide a corrosion resistant pump in accordance with this invention.

It is a primary object of the present invention to provide an improved pump for use with corrosive materials wherein the pump chamber is fully sheathed with PTFE.

Another object of the present invention is to provide an improved corrosion resistant centrifgual pump having an encapsulated impeller, i.e., one which is fully coated with PTFE.

Another object of the present invention is the provision of a centrifugal pump for corrosive chemical service wherein all portions of the wet end of the pump contacted by corrosive liquids are coated with a corrosion resistant coating of PTFE.

Another object of the present invention is the provision of a pump of the type described wherein the wet end of the pump chamber is sheathed in PTFE and wherein the sheaths are anchored to prevent movement thereof in response to variations in temperature.

Another object of the present invention is the provision of a self-priming centrifgual pump wherein all fluid contacted surfaces of the wet end are sheathed with a corrosion resistant liner of PTFE.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

4 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in side elevation of a pump in accordance with the present invention;

FIG. 2 is a view in front end elevation of the pump of FIG. 1, looking from the right of FIG. 1;

FIG. 3 is a view partly in section and partly in elevation taken generally along the line 33 of FIG. 2;

FIG. 4 is an enlarged fragmentary section of the portion of FIG. 3 showing the joint between the casing and the rear cover;

FIG. 5A is an enlarged fragmentary section of the seal assembly shown in FIG. 3;

FIG. 5B is an enlarged section of another type of seal assembly usable in accordance with the present invention;

FIG. 6 is a view partly in section and partly in elevation taken essentially along the line 66 of FIG. 3;

FIG. 7 is a view in section taken essentially along the line 77 of FIG. 6;

FIG. 8 is a plan view of the discharge end of the P p;

FIG. 9 is a plan view of a PTFE coated impeller in accordance with the present invention, with a portion thereof broken away;

FIG. 10 is a side view in section taken along the line 10-10 of FIG. 9;

FIG. 11A is a view in section of the sheath for the casing as formed and before assembly thereto;

FIG. 11B is a view in section of the sheath for the rear cover as formed and before assembly thereto;

FIG. 12 is a view partly in section and partly in elevation of a self-priming centrifgual pump in accordance with this invention; and

FIG. 13 is an end view, partly in section and partly in elevation, with portions of the inlet side of the pump removed, of the self-priming pump in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, which illustrate a preferred form of the invention, FIGS. 1 and 2 show a pump 10 operated by a motor 11, the two being interconnected by a drive shaft 12 and a coupling unit 13, the latter connected in driving relation to an impeller drive shaft 15. The drive shaft 15 is supported by a bearing housing 16 containing a. bearing assembly, not shown.

The pump includes a casing 17 and a rear cover assembly 18 which form therebetween a chamber 20 ,(FIG. 3). In the form shown, the casing 17 includes an inlet 2.1 and an outlet 22 each receiving

conduits

23 and 24, respectively and forming a supply line and a discharge line. The rear cover assembly 18 is secured to the casing 17 by bolts 25. The motor 11, the bearing unit 16 and casing 17 are individually supported by

feet

26, 27 and 28, respectively, which are bolted to a fixed base 29 in the usual way. The bearing housing 16, the internal details of which are shown in US. Pat. No. 3,169,486 of Feb. 16, 1965, and assigned to the same assignee, includes a plurality of fingers 30 which are bolted to the rear cover plate 18 by bolts 31.

Referring to FIG. 3, the interior fluid contacted surface portions of the casing 17 include a sheath thereon of PTFE which is of sufficient thickness to prevent passage through the sheath of corrosive materials. The sheath 35 includes an integral neck portion 36 extending through the inlet opening 21 and a flared portion 36a engaging a flange 37 on the inlet. As shown, flange 37 includes screw threads and is recevied over the threaded inlet end of the pump, as shown. The outlet end also includes a flange 38 which receives a flared end 39 of a second integral neck portion 40 (FIG. 6) of the sheath or liner 35 received on the surface of casing 17.

The rear cover plate 18 is provided with an opening 42 through which the drive shaft 15 of the impeller extends.

All fluid contacted surfaces of the cover plate 18 are covered with a second sheath 45 of PTFE which is sufficiently thick to prevent passage therethrough of corrosive materials. Each of the sheaths or

liners

35 and 45 include outer

peripheral portions

35a and 45a which are in facing relation and which operate to seal the rear cover 18 to the casing 17. The casing includes an annular undercut 46 (FIG. 4) to form an annular lip 47, the peripheral portion 35a of the sheath being received in the undercut. During assembly of the pump parts the lip 47 aids in maintaining the peripheral portion 35a in place. The face 49 of the casing opposite the rear cover includes a series of continuous annular ridges and grooves 50 and 51, respectively, which extend all the way around the face 49 of the casing. The rear cover plate 18 includes a facing portion 53, positioned opposite the face 49, and having a series of continuous annular ridges and

grooves

55 and 56, respectively, which likewise extend all the way around the facing portion of the rear cover. As shown, the facing portion 53 of the rear cover is of a diameter a few thousandths of an inch smaller than the radial dimension of the lip for interfitting relation with the casing.

The differences in height between the grooves and ridges may be as much as A inch or more depending on the cross-sectional thickness of the sheath and the size of the pump, although such grooves and ridges may have a difference in height as small as .005 to .010 of an inch. These grooves and ridges may be interrupted, if desired, although it is easier to form them as continuous elements.

During the assembly of the sheath or liner to the casing and rear cover, the

peripheral portions

35a and 45a of the sheaths are forced into the corresponding grooves allow ing the ridges to bite into the PTFE. Although other forms of securing the peripheries may be used, this arrangement securely anchors the peripheral portions of both sheaths to prevent movement thereof radially inwardly. Moreover, the pattern of ridges and grooves forms a series of high and low pressure seal areas corresponding to the portions overlying the ridges and those overlying the grooves, respectively. By providing a close fitting between the face 53 of the rear cover and the face 49 of the casing, extrusion of the PTFE radially outwardly is prevented. The portion of the PTFE overlying the grooves is at a lower sealing pressure and functions to pro wide a relief for expansion thereof, as described in US. Pat. No. 3,212,411, issued Oct. 19, 1965, and assigned to the same assignee. Thus, the

peripheral portions

35a, 45a of the sheaths are anchored at one end, and in the case of sheath 35, is effectively anchored by securing

neck portions

36 and 40 in the inlet and outlet passages by the holding action of the corresponding flared portions which are clamped between flanges and the associated conduit.

The opening 42 of the rear cover includes an annular shoulder 60 having a shallow annular counterbore 61 therein. Received in the opening 42 between the rear cover 18 and the shaft 15 is a corrosion resistant seal seat 65 which is generally T-shaped in cross-section and which engages an inner peripheral portion 66 of sheath 45 to force a portion of the sheath into the counterbore 61 for anchoring the inner peripheral portion of the sheath. The annular seal seat 65 is clamped against the rear cover by clamp ring 68 which is held in place by studs 69,

annular cushioning gasket 70 being placed therebetween (FIG. A). The seal seat 65 is of ceramic, tungsten carbide or carbon.

The inner peripheral portion 66 of the sheath is thus clamped and prevented from moving radially inwardly. In this way, both peripheries of the sheath are held firmly in place to prevent their movement during temperature cycling.

Since PTFE has a coefi'icient of thermal expansion greater than most metals, provision is made for relief areas in the chamber 20 to accommodate the growth of the PTFE in response to increases in temperature. Ac-

cordingly, the casing 17 includes on its inner surface a generally annular relief area into which the PTFE may move or grow thus substantially preventing permanent deformation as a result of PTFE growth due to increasing in temperature. It is to be understood that other forms of relief areas may be used as will'be apparent to those skilled in the art.

Received Within the chamber 20 is an impeller of the open impeller type and provided with a hollow threaded shank 81 which receives the threaded end of the drive shaft 15, as shown. The outer surface of the im peller 80 is coated with PTF-E coating 82 formed over a metal impeller blank 83 to form an encapsulated impeller. The outer surface of the blank includes a PTFE sleeve 84, integral with the coating 82 and extending over a bearing surface 85 formed on the impeller drive shaft 15.

Referring to FIG. 5A, the shaft 15 is sealed to the rear cover assembly 18 by a bellows type seal including a r0- tating annular sealing member urged into engagement with the sealing face of the annular seal seat 65, of corrosion resistant material, which is clamped in place to the rear cover. The rotatable portion of the seal member is urged into engagement with the seal seat by a plurality of springs 91 which hear at one end against a spring retainer 93 and at the other end against spring adapter 94 mounted on a clamp ring 95 secured to the shaft and rotatable therewith. The sealing member 90 includes PTFE bellows 96, one end 96a of which is clamped to the shaft by ring 95 and the other end 96b of which is secured and sealed to scaling member 90 through a support ring 97.'

This type seal structure per se is known.

The seal element 90 prevents passage of fluid between it and the seal seat 65 while the sealed bellows assembly 96 affixed to the rotating clamp ring 95 prevents passage of fluid between the shaft and end 96a of the bellows.

Referring to FIG. 5B, wherein like reference numerals have been employed where applicable, a rotatable mechanical seal is shown in which a rotating movable seal element 100 is urged into engagement with the seal seat 65 by a plurality of springs 102 through an annular disk 103 which tends to compress an annular PTFE ring 104 which is generally triangular in cross-section as shown. The rotating portion of this seal is fixed to the shaft 15 by a compression type coupling 105.

Other forms of seals may be used as will be apparent to those skilled in the art, for example, double internal mechanical seals, single internal seals, and the like.

Referring to FIGS. 6-8, the pump chamber 20 is in the form of a volute with all portions of the chamber being covered with a corrosion resistant sheath of polytetrafluoroethylene as indicated previously. The shank 81 of the impeller receives the threaded end of the impeller shaft 15, the shank being covered by a sleeve of PTFE 84 which is integrally formed with the sheath 82.

The outlet 22 of the pump is formed with a split coupling, one portion 106 being integral with the casing and the other 107 being bolted to the casing by bolts 108. The two parts of the coupling being aligned by pins 109 and form the flange which receives the flared portion 39 of the sheath 35. As shown in FIG. 7, a portion of the ridges 50 and groves 51 are formed on half coupling 107 and are in alignment with the grooves and ridges formed on the casing.

Referring to FIGS. 9 and 10, the corrosion resistant PTFE encapsulated impeller structure 80 is shown. As illustrated, the impeller is of the open type and includes a metal impeller blank 83, the blank 83 being in the form of an impeller and including blade elements 110'. All surfaces of the impeller blank are covered with/a PTFE coating 82. The impeller blank also includes a hollow threaded shank 81 with a sleeve portion 84 of the PTFE sheath 82 forming a lining which extends beyond the end of the shank 81. The sleeve 84 is integral with the sheath 82 but of somewhat reduced cross-sectional thickness as shown in FIG. 10.

The

sheaths

35 and 45 and the sheath 82 on the impeller are formed by an isostatic coating process, the details of which are described in U.S. patent application Ser. No. 497,869, filed Oct. 19, 1965, now U.S. Pat. No. 3,459,213, and assigned to the same assignee.

Referring to FIGS. 11A and 11B,

sheath blanks

115 and 120, corresponding to sheaths 35 and 45, respectively, are formed isostatically in a predetermined configuration corresponding essentially to the configuration the respective sheaths have in the assembled pump, as is apparent from comparison of FIGS. 3 and 11A and 11B. Since the sheath blanks are sintered in the configuration shown, they have a primary memory of this configuration, i.e., this is a stable configuration over quite a range of temperatures. During assembly of the sheaths to the corresponding pump parts, portions thereof are worked to change the configuration slightly from the formed configuration. Specifically, sheath blank 115 is assembled to a casing and

portions

116 and 117 are flared to form

flanges

36a and 39, respectively. Portion 118 of the blank 115 is flared outwardly, tucked into the undercut 46 to form the outer periphery 35a and pressure is applied to force the PTFE into the ridges and grooves as previously described. Since

portions

116, 117 and 118 of the blank 115 have been worked to change their configuration from the predetermined formed configuration,

portions

36a, 39 and 35a have a secondary memory of their shape in the casing and a primary memory of their formed configuration, as shown in FIG. 11A.

In the case of sheath blank 120, portion 121 is flared outwardly to form the inner periphery 66 while portion 122 is pressed against face 53 of the rear cover to force the PTFE into the ridges and grooves as previously described.

Accordingly, the portions of the

sheaths

35 and 45 which have been worked, and which have both primary memory of their formed configuration and a secondary memory of their worked configuration are securely anchored to prevent changes in configuration due to temperature cycling. It is to be noted, however, that those portions of the sheaths which are contacted by fluid being pumped have only a primary memory and need not be locked to the corresponding portions of the casing and rear cover when used in the temperature range of -20 F. to +400 F. Thus, by providing sheaths whose fluid contacted surfaces have a predetermined formed configuration corresponding to the configuration of the pump chamber, and thus a primary memory of the predetermined configuration, unusual temperature stability is achieved.

As shown in FIG. 11A, the

neck portions

36 and 40 are integral with the sheath blank 115, and the flanges are formed during assembly, as noted previously. For this reason, the outlet portion of the pump utilizes a split coupling, previously described and a threaded flange 37 i on the inlet side, the flange 37 being adjusted so as to engage the flange 36a on the inlet portion of the pump.

The sheath 82 on the impeller is also formed by the isostatic molding procedure described in the previously identified application. Here too, sheath 82 has a primary memory of the shape in which it was sintered, that is, essentially the shape of the impeller and therefore exhibits considerable stability to temperature over a wide range.

The advantages of forming the parts isostatically are described fully in U.S. application Ser. No. 497,869, and this procedure offers a convenient way of forming a sheath on a complex shape. After the sintering operation, the sheaths may be machined to final dimensions, if needed, and in the case of sheath 82 formed on the impeller 80, the tip end of the impeller blades and the forward faces 110 are machined to final dimensions.

Tests on pumps in accordance with the present invention established that the operating parameters were significantly better than originally anticipated. For example,

an efliciency of 60% for a pump having a three inch diameter inlet and a 1% inch diameter outlet end is Percent G.p.1n. elllciency Corrosion tests were also run on pickling solution used to clean stainless steel castings. This solution is extremely corrosive and cotnains 4% hydrofluoric acid and 20% nitric acid, the solution being at a temperature of 150 F. The pump having the above dimensions and operating at 1750 r.p.m. and generating a head of 48 feet at about 20 gallons per minute was run for over hours on pickling service. During shut down periods, the lined pump parts were immersed in the pickling solution for about 500 hours. The pump was disassembled and examined and showed no appreciable corrosion.

Temperature cycling tests in hot oil established the dimensional stability of all the parts.

Referring to FIGS. 12 and 13, a self-priming centrifugal pump is shown including a priming chamber mounted to the inlet end 21 of the pump and an air separator 137 mounted to the outlet end 22 of the pump, the internal details of the pump having been previously described. Positioned within the air separator 137 is an air separator tube 138, the air separator 137 and the pump chamber being interconnected by a by-pass line 139. As shown, all internal surfaces of the priming chamber are coated with a corrosion resistant sheath 140 of PTFE, and all internal surfaces of the air separator 137 are likewise coated with a corrosion resistant sheath 142 except for the air separator tube 138 which may be made of corrosion resistant metal.

The priming chamber is formed of two separate castings 144 and 145, the two castings being essentially of the same configuration and bolted together. The sheaths 140 include

flanges

146a and 146b, the casting being provided with a priming chamber cover 150 which is clamped in sealing relationship through a gasket 151 to an opening 155 formed therein. As shown, the portion 156 of sheath 140 which covers the priming chamber cover is likewise flanged to form a seal.

The sheath 142 of the air separator includes a flared end 158 at the exit end of the air separator, and is also flared at the inlet end 159 thereof which is connected to the outlet end of the pump. By-pass line 139 is in the form of a stainless steel braid covered PTFE line mounted on the by-pass line mounting assembly 160 which likewise includes a flared portion 161 of sheath 142. As shown, the pump chamber includes a by-pass line connection with a side opening 165 formed therein, opening 165 including an integral portion 166 of the sheath 35, a flared section 167 being provided for sealing purposes between the bypass line and the mounting on the chamber.

The casing and rear cover, and the other parts forming the wet end of the pump may be of ductile iron or high strength plastic.

The features of the present invention while described with reference to a centrifugal pump may also be used for in-line pumps, positive displacement pumps, and the like, in which a pumping element rotates within a fully sheathed pump chamber.

It is also understood that while the pump of the present invention is usable as a corrosion resistant pump, it finds use in other fields and services such as those previously mentioned.

By the present invention, the need for interchangeable wet ends of different materials in centrifugal pumps is substantially eliminated by the use of corrosion resistant lining which offers resistance to a wide variety of chemicals. Thus, the metallic elements of the casting need not be fabricated of the hard to cast materials such as the high silicon iron alloys. The pump of the present invention also exhibits good performance characteristics com pared to conventional centrifugal pumps, and superior performance characteristics as compared to centrifugal pumps utilizing a liner of a fluorocarbon copolymer.

While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention.

What is claimed is:

1. In a pump for use with corrosive materials wherein said pump includes a casing and a cover assembly defining therebetween a chamber through which fluid is pumped, a pumping element received within said chamber and cooperating therewith to force fluid through said chamber, drive shaft means extending within said chamber and connected to said pumping element for effecting rotation thereof within said chamber, said chamber including means communicating therewith and forming an inlet and an outlet for fluid being pumped, the diameter each of said inlet and outlet being less than the diameter of said chamber, each of said inlet and outlet means including means for connection to conduit means, seal means cooperating with said shaft to prevent leakage of fluid between said shaft and said chamber, a first and second polytetrafluoroethylene sheath one covering all fluid contacted surfaces of said casing and the other covering all fluid contacted surfaces of said cover assembly, each of said sheaths being a unitary structure and said sheaths including first and second neck portions extending respectively through said inlet and outlet means, said sheaths and neck portions cooperating to provide a chamber and inlet and outlet means fully lined with polytetrafluoroethylene, said first and second sheath including cooperating peripheral portions forming a seal therebetween, means securing the peripheral portions of said sheaths against radial movement, said second sheath including an inner peripheral portion secured to said cover against radial movement, said sheaths being sufliciently thick to provide corrosion resistance, and the portion of each of said sheaths contacted by fluid being pumped having a predetermined configuration corresponding essentially to the configuration in said chamber, the said portion of each said sheath having a primary memory of said predetermined configuration. for maintaining said configuration in response to increase in temperature.

2. A pump as set forth in claim 1 wherein said chamber includes means forming a relief area into which polytetrafluoroethylene may move in response to changes in temperature thereby substantially eliminating permanent distortion thereof.

3. A pump as set forth in claim 1 wherein the periphera1 portions of said sheaths have a secondary memory.

4. A pump as set forth in claim 1 wherein said pump is a centrifugal pump and wherein said pumping element is an impeller.

5. A centrifugal pump as set forth in claim 4 wherein said first sheath covers said casing, said second sheath covering said cover assembly, said inlet and outlet means being provided in said casing, and said first and second neck portions being provided in said first sheath.

6. A centrifugal pump as set forth in claim 4 wherein said impeller means is of a corrosion resistant metal.

7. A centrifugal pump as set forth in claim 5 wherein said impeller means is encapsulated in polytetrafluoroethylene.

8. A centrifugal pump as set forth in claim 8 wherein said impeller means includes a shaft section extending through said cover plate, at least the portion of said shaft section extending through the cover plate including a sheath of PTFE on the outer surface thereof, said sheath on said shaft section being integral with the sheath on said impeller.

9. A centrifugal pump as set forth in claim 9 wherein said cover assembly includes a shoulder formed in the surface thereof opposite said chamber and surrounding said shaft, the inner peripheral portion of said second sheath being received on said shoulder, stationary seal seat means surrounding said shaft and urging the peripheral portion of said second sheath into engagement with said cover assembly, and said seal means being mechanical seal means cooperating With said seal seat and shaft to prevent passage therethrough of fluid being pumped.

10. A centrifugal pump as set forth in claim 5 wherein said inlet means is located in axial alignment with said impeller means, and said outlet means being located radially of said impeller means.

11. A centrifugal pump as set forth in claim 4 wherein said means securing the peripheral portions of said sheaths includes concentric grooves formed in the facing peripheral portion of said cover assembly and said casing, and the peripheral portions of said sheaths including lands received in said grooves.

12. A pump as set forth in claim 4 wherein said pumping element includes an outer sheath of PTFE on all fluid contacted surfaces thereof.

13. A centrifugal pump as set forth in claim 7 wherein said impeller means is an open impeller.

14. A centrifugal pump as set forth in claim 4 further including a priming chamber and an air separator, PTFE sheath means covering all fluid contacted surfaces of said priming chamber and said air separator, and corrosion resistant by-pass means interconnecting said chamber and said air separator for providing a self-priming pump.

References Cited UNITED STATES PATENTS 2,400,234 5/1946 Hudson 103-114 1,578,236 3/1926 La Bour 1031 13 2,466,812 5/ 1949 Jacobsen 1031 13 2,695,246 11/1954 Jurgensen Jr., et al. l03-114 3,037,458 6/1962 Olmstead et al. 103111 3,238,881 3/1966 Camac 1031 14 3,265,002 8/1966 Warman 103103 3,358,609 12/1967 Worth et al 103114 FOREIGN PATENTS 680,004 2/1964 Canada 415-173 1,092,549 11/1954 France 415-196- 1,314,736 12/1962 France 415172 426,523 4/1935 Great Britain 4l5-173 885,349 12/1961 Great Britain 415197 HENRY F. RADUAZO, Primary Examiner U.S. Cl. X.R. 415197, 204

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,551,067 Dated December '29, 1970 Jack L. Wissman Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 5, "increasing" should be increases--. Column 6, line 14, "blank" should be shank-.

Column 8, line 20, correct the spelling of "contains". Column 9 line 34, following "chamber," insert the improveme comprising-. Column 10, line 5, "claim 5" should be claim 4; line 8, "claim 8" should be claim 7; line 15, "claim 9" should be claim 8; line 25, "claim 5" should be claim 4-.

Signed and sealed this 8th day of June 1971.

(SEAL) Attest:

EDwARD-M.FIETGHER,J'R. WILLIAM E. SGHUYLER, J Attesting Officer Commissioner of Patent