GB1574610A

GB1574610A - Piston-type valves and plunger pumps

Info

Publication number: GB1574610A
Application number: GB3212176A
Authority: GB
Original assignee: Ricardo Consulting Engineers Ltd
Current assignee: Ricardo PLC
Priority date: 1977-08-02
Filing date: 1977-08-02
Publication date: 1980-09-10

Description

(54) PISTON-TYPE VALVES AND PLUNGER PUMPS (71) We, RICARDO CONSULTING ENGINEERS LIMITED, a Company registered under the Laws of England, of Bridge Works, Shoreham-by-Sea Sussex BN4 SFG, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be per formed, to be particularly described in and by the following statement: This invention relates to piston-type valves and plunger pumps of the kind in which the movable valve/pump member comprises a usually-cylindrical piston or plunger, re ferred to herein as the plunger, which is reciprocated longitudinally in a bore. The invention is particularly although not ex clusively applicable to pumps or valves of this kind used for pumping or controlling flows of gases, and concerns the sealing of the plungers of such valves and pumps.

Small piston valves are widely used as relays in servomechanisms, but they are also frequently used as shuttle or spool valves in applications in which they again function as timing or positioning valves but operate at a much higher frequency. When such valves are used in hydraulic circuits, seal ing of the valve piston or spool is effected by the use of very fine tolerances on the sealing lands, and the lubricating effects of the hydraulic fluid is usually sufficient to avoid seizure or wear, particularly if the pressure is applied uniformly around the circumference of the piston or spool to prevent "hydraulic lock" due to transverse loading on the piston or spool.

When such piston valves are used to con trol the flow of gases which must be kept free from oil, problems of material com patibility, lubrication and wear can arise.

Such problems are aggravated by the need for very fine clearances to avoid excessive leakage of low viscosity gases.

According to the present invention, a piston valve or plunger pump of the kind specified comprises a longitudinally-recipro cable plunger slidable in a liner sleeve mounted in a cylindrical bore in a rigid valve or pump housing, the liner sleeve being a tube having at least one external circumferential groove housing an 0being which seals against the surrounding surface of the cylindrical bore in the housing, the wall thickness of the liner sleeve at the base of the groove being such that the liner sleeve is radially deformable inwardly at this loca tion by the inward pressure of the O-ring into sealing contact with the surface of the piston or plunger.

The plunger preferably is a generallycylindrical metal member, or example made of stainless steel, and the liner sleeve is preferably of synthetic plastics material, e.g. glass-filled polytetrafluoroethylene.

In the case of a piston valve the plunger may be formed with one or more circum ferential grooves whose side walls diverge outwardly and intersect its surfaces obliquely, for example each at an internal angle of about 1700 with the said surface.

The invention may be carried into prac tice in various ways, but one specific em bodiment thereof will now be described by way of example only and with reference to the accompanying drawings, in which : Figures 1, 2 and 3 are views in longi tudinal section of a piston valve, respec tively showng the valve plunger in three different operating positions, and Figure 4 is a detailed view on a larger scale showing the sealing arrangement for the valve plunger.

In the illustrated embodiment a piston valve is employed as a metering valve to connect a vacuum-operated diaphragm pump alternately to a vacuum source and to a positive pressure to drive the diaphragm pump, the valve plunger being reciprocated longitudinally by an electric motor. The valve illustrated comprises a rigid cylindrical plunger 10 made of stainless steel which can be slidably -reciprocated longitudinally in a cylinder bore 11 formed in a rigid metal valve housing 12, the cylinder bore 11 being lined with a tubular sleeve or barrel 13 made of 25%-glass-filled polytetrafluoroethylene.

The plunger 10 is coupled to the associated electric motor by which it is longitudinallyreciprocated, and is formed with circum ferential grooves 14 separated by a land i5, and cooperates with longitudinally-spaced ports 16, 17, 18 formed in the liner sleeve 13 in register with gas passages 161, 17ì, 181 formed in the valve housing 12. As shown, the opposite side walls 19 of each groove 14 diverge outwardly and each intersects the cylindrical surface of the plunger obliquely, at an internal angle 10 therewith of 1700 or more, i.e. an included angle of 20 or less between the two divergent side walls 19. The plunger 10 is provided with a fine surface finish and is polished longitudinally, and will satisfactorily run completely dry in the p.t.f.e. liner, even when reciprocated at a frequency of 30 Hertz for a prolonged period. If the gas flow being controlled is wet, the choice of stainless steel for the plunger material and glass-filled p.t.f.e. for the cylinder liner will avoid any difficulties over corrosion.

The liner sleeve 13 is formed with four external circumferential grooves 20 of approximately square cross-section, one near each end and one on either side of the central port 17, and an O-ring 21 is fitted in each groove 20. Each O-ring is made of the synthetic resilient sealing material known by the trade name VITON, which is oil resistant and will not swell should any lubricating oil or fuel contamination happen to occur in service. As shown each of the grooves 20 extends upwardly through the major part of the wall thickness of the liner sleeve 13, leaving only a thin section of the wall below its radially-inner surface. The O-rings bear resiliently against the surrounding surface of the cylinder bore 11, and as shown in detail at 22 in Figure 4 each O-ring by its radially-inward resilient pressure de forms the thin wall section of the liner sleeve beneath it in the radially-inward direction, producing an inwardly-protruding annular constriction in the bore of the liner sleeve which seals against the stainless steel plunger 10. It has been found that with the obliquely intersecting side walls 19 of the grooves 14 in the plunger, the seal thus formed operates satisfactorily without appreciable wear even when the plunger is dry-reciprocated for extended working periods.

Thus a prototype valve according to the drawings has operated on test for some 100 hours with a stroke of 0.5 inch at a dry reciprocation frequency of 30 Hertz with no sealing or wear problems. In actual service the reciprocation frequency of the valve in this particular diaphragm pumn -application would be only 10 Hertz. In such applications where the valve is used for metering gas flows, the absence of any contained volumes associated with the plunger sealing, such as would fill with the gas being controlled and thus affect the metering, is an advantage.

However the invention is also applicable to other applications of piston valves and plunger pumps of this general kind, for example to plunger pumps used in the preparation of foods where the absence of complicated plunger seals will aid cleaning.

WHAT WE CLAIM IS:- 1. A piston valve or plunger pump of the kind specified which comprises a longitudinally-reciprocable plunger slidable in a liner sleeve mounted in a cylindrical bore in a rigid valve or pump housing, the liner sleeve being a tube having at least one external circumferential groove housing an O-ring which seals against the surrounding surface of the cylinder bore in the housing, the wall thickness of the liner sleeve at the base of the groove being such that the liner sleeve is radially deformable inwardly at this location by the inward pressure of the O-ring into sealing contact with the surface of the plunger.

2. A valve or pump as claimed in Claim 1, in which the liner sleeve is made of synthetic plastics material.

3. A valve or pump as claimed in Claim 2, in which the liner sleeve is made of glassfilled polytetrafluoroethylene.

4. A valve or pump as claimed in Claim 1 or Claim 2 or Claim 3, in which the plunger is a generally-cylindrical metal member.

5. A valve or pump as claimed in any one of Claims 1 to 4, in which the plunger is made of stainless steel.

6. A valve or pump as claimed in any one of the preceding claims, in which the liner sleeve has a plurality of the external circumferential grooves along its length, each housing a respective O-ring.

7. A piston valve as claimed in any one of the preceding claims, in which the plunger is formed with one or more circumferential grooves whose side walls diverge outwardly and intersect its surface obliquely.

8. A piston valve as claimed in Claim 7 in which the side walls of the or each groove intersect the surface of the plunger each at an internal angle of about 1700 with the said surface.

9. A piston valve substantially as specifically described herein with reference to the accomopanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

The plunger 10 is coupled to the associated electric motor by which it is longitudinallyreciprocated, and is formed with circum ferential grooves 14 separated by a land i5, and cooperates with longitudinally-spaced ports 16, 17, 18 formed in the liner sleeve

13 in register with gas passages 161, 17ì,

181 formed in the valve housing 12. As shown, the opposite side walls 19 of each groove 14 diverge outwardly and each intersects the cylindrical surface of the plunger obliquely, at an internal angle 10 therewith of 1700 or more, i.e. an included angle of 20 or less between the two divergent side walls 19. The plunger 10 is provided with a fine surface finish and is polished longitudinally, and will satisfactorily run completely dry in the p.t.f.e. liner, even when reciprocated at a frequency of 30 Hertz for a prolonged period. If the gas flow being controlled is wet, the choice of stainless steel for the plunger material and glass-filled p.t.f.e. for the cylinder liner will avoid any difficulties over corrosion.

The liner sleeve 13 is formed with four external circumferential grooves 20 of approximately square cross-section, one near each end and one on either side of the central port 17, and an O-ring 21 is fitted in each groove 20. Each O-ring is made of the synthetic resilient sealing material known by the trade name VITON, which is oil resistant and will not swell should any lubricating oil or fuel contamination happen to occur in service. As shown each of the grooves 20 extends upwardly through the major part of the wall thickness of the liner sleeve 13, leaving only a thin section of the wall below its radially-inner surface. The O-rings bear resiliently against the surrounding surface of the cylinder bore 11, and as shown in detail at 22 in Figure 4 each O-ring by its radially-inward resilient pressure de forms the thin wall section of the liner sleeve beneath it in the radially-inward direction, producing an inwardly-protruding annular constriction in the bore of the liner sleeve which seals against the stainless steel plunger 10. It has been found that with the obliquely intersecting side walls 19 of the grooves 14 in the plunger, the seal thus formed operates satisfactorily without appreciable wear even when the plunger is dry-reciprocated for extended working periods.

Thus a prototype valve according to the drawings has operated on test for some 100 hours with a stroke of 0.5 inch at a dry reciprocation frequency of 30 Hertz with no sealing or wear problems. In actual service the reciprocation frequency of the valve in this particular diaphragm pumn -application would be only 10 Hertz. In such applications where the valve is used for metering gas flows, the absence of any contained volumes associated with the plunger sealing, such as would fill with the gas being controlled and thus affect the metering, is an advantage.

However the invention is also applicable to other applications of piston valves and plunger pumps of this general kind, for example to plunger pumps used in the preparation of foods where the absence of complicated plunger seals will aid cleaning.

WHAT WE CLAIM IS:- 1. A piston valve or plunger pump of the kind specified which comprises a longitudinally-reciprocable plunger slidable in a liner sleeve mounted in a cylindrical bore in a rigid valve or pump housing, the liner sleeve being a tube having at least one external circumferential groove housing an O-ring which seals against the surrounding surface of the cylinder bore in the housing, the wall thickness of the liner sleeve at the base of the groove being such that the liner sleeve is radially deformable inwardly at this location by the inward pressure of the O-ring into sealing contact with the surface of the plunger.
2. A valve or pump as claimed in Claim 1, in which the liner sleeve is made of synthetic plastics material.
3. A valve or pump as claimed in Claim 2, in which the liner sleeve is made of glassfilled polytetrafluoroethylene.
4. A valve or pump as claimed in Claim 1 or Claim 2 or Claim 3, in which the plunger is a generally-cylindrical metal member.
5. A valve or pump as claimed in any one of Claims 1 to 4, in which the plunger is made of stainless steel.
6. A valve or pump as claimed in any one of the preceding claims, in which the liner sleeve has a plurality of the external circumferential grooves along its length, each housing a respective O-ring.
7. A piston valve as claimed in any one of the preceding claims, in which the plunger is formed with one or more circumferential grooves whose side walls diverge outwardly and intersect its surface obliquely.
8. A piston valve as claimed in Claim 7 in which the side walls of the or each groove intersect the surface of the plunger each at an internal angle of about 1700 with the said surface.
9. A piston valve substantially as specifically described herein with reference to the accomopanying drawings.