GB2113357A

GB2113357A - Pressure relief valve

Info

Publication number: GB2113357A
Application number: GB08300401A
Authority: GB
Inventors: Jurgen Steinmuller
Original assignee: PFEIFFER VAKUUMTECHNIK; Arthur Pfeiffer Vakuumtechnik Wetzlar GmbH
Current assignee: PFEIFFER VAKUUMTECHNIK; Arthur Pfeiffer Vakuumtechnik Wetzlar GmbH
Priority date: 1982-01-09
Filing date: 1983-01-07
Publication date: 1983-08-03
Also published as: DE3200471A1; GB8300401D0; GB2113357B

Abstract

The pressure relief valve is biassed by weight, in particularly for use with rotary piston pumps and pump units, and opens when the pressure difference exceeds a maximum permitted value. The damping of the valve 12 is achieved by one or more rectangular rings 11, which are fitted on a cylindrical piston 6 within a valve guide 9. <IMAGE>

Description

SPECIFICATION Pressure relief valve The invention concerns a pressure relief valve biassed by weight, preferably for insertion in vacuum pumps or pump combinations, particularly rotary piston pumps, in order to protect the pumps or parts thereof from excess pressure.

Pressure relief valves are used in vacuum pumps and pump units to effect pressure equalisation between the individual stages or between one stage and atmosphere. They can be built in either between individual pumps or pump stages or directly between the suction inlet and pressure outlet of a pump, in particular or a rotary piston pump. In the latter case, the pressure relief valve is very often an integral part of the pump. In this case we are dealing with a valve biassed by weight, which opens or closes when the pressure difference exceeds or drops below a maximum permitted value.

When constructing vacuum pump units, the suction power of the individual vacuum pumps are graduated downwards in order to achieve better efficiency. This is particularly the case with rotating disc pumps and rotary piston pumps, and when there are several rotary piston pumps in series. If the pumps are connected together, an excess pressure builds up on the pressure outlet side of the following rotary piston pumps,due to the usual limited suction power of the previous pump. After the pressure difference exceeds a predetermined value, the pressure relief valve opens. The gases not taken from the previous pump flow from the pressure side of the following rotary piston pump to atmosphere, or through a channel back to the suction inlet of the rotary piston pump.This occurs until, due to the falling suction pressure, the predetermined pressure difference value at the pressure relief valve is no longer exceeded, and the valve shuts again.

Valves of this kind are known and are built into vacuum pumps and pump units, in particular in rotary piston pumps. For example, in German Offenlungsschrift 2844019 a rotary piston pump with a pressure relief valve is described, which is arranged at an angle of 45 to the direction of flow in the pump. This has the disadvantage that the force derived from the weight is divided into two components. Thus, only a part of the force is available as a real closing force for the pressure relief valve.

The common disadvantage of the previously existing pressure relief valves biassed by weight, particularly when used with rotary piston pumps, is that the natural frequency of the valve body is easily excited by the pulsing medium flow. This gives rise to powerful vibrations, going so far as damage or destruction of the valve or the pump. Therefore, the valve body must be damped. This damping is achieved, in the existing valves using friction rods made of Teflon-Bronze which are pressed by a spring against a guide post. The disadvantage of the construction is the easy dirtying of the friction rods, and their relatively high cost.

In the arrangement shown in German Offenlegungsschrift 28 44 019, damping is only achieved at very heavy technical expense requiring gaps accurate to several hundredths of a millimeter) with bearing boxes of PTFE.

These wear easily in operation, and due to the fact that they are easily dirtied, they can only be used to a limited extent in the chemical industry. The present invention is the based on the problem of proposing a pressure relief valve biassed by weight for vacuum pumps and pump sets, in particular for rotary piston pumps, in which the described disadvantages, particularly the deficient damping, are reduced or avoided.

Accordingly, the invention proposes a pressure relief valve in a rotary piston pump which is arranged between the suction inlet and the pressure outlet of a pump stage and which opens if the pressure difference exceeds a maximum permitted value, wherein the valve is positioned vertically and is damped by one or more rectangular piston rings on a cylindrical piston within a cylinder sleeve, said value being determined by the weight of the piston, the rings and any weights placed on the piston. The accuracy of production of the valve parts does not need to be very high.

The damping is produced by the axial resilience of the rectangular rings. The energy absorbed in the damping when the valve moves is converted at the cylinder wall into frictional heat and carried away. Only minimum gaps between the piston and cylinder.

Thus, a subsidiary damping effect is achieved by the enclosed volume of air. This effect is particularly large when the pressures reach valves of the order of atmospheric pressure, and is particularly useful for the damping of large pressure shocks.

The difference in pressure at which the valve opens or closes can be set by alteration by the weight loading, for example by adding or removing rings or discs.

The invention will be more clearly described with reference to the following figures, showing an exemplary embodiment thereof. The drawings show: Figure 1: Pressure relief valve with rectangular rings; Figure 2: Rotary piston pump with a pressure relief valve integral with the side part; Figure 3: A rotary piston pump with a pressure relief valve in the middle section; and Figure 4: A rotary piston pump with a pressure relief valve in a separate duct.

The pressure relief valve is shown in Fig. 1 in section. A cylindrical piston 6 slides in a cylinder sleeve 9, which serves as a valve guide and is closed with a cover 10. The valve plate 1 2 separates the suction inlet 2 from the pressure outlet 3 of a vacuum pump.

The necessary bias to determine the critical pressure is achieved by placing weights on the piston 6. The latter is provided with two piston rings 11 of rectangular cross-section.

These may also be of pre-determined weight and thus form an element of the bias. The rings may be sprung outwards to increase their frictional effect and improve damping.

In Fig. 2, the pressure relief valve is an integrated part in the side section 8 of a rotary piston pump 1. It serves to divide the connection channel 4 between the suction inlet 2 and the pressure outlet 3 of a rotary piston pump. The cylinder sleeve forming a valve guide is here provided by the valve housing.

In the arrangement shown in section in Fig.

3, the by-pass connecting channel 4 between the suction inlet 2 and the pressure outlet 3 of a rotary piston pump 1 has the pressure relief valve 7 directly at the middle part of a pump housing 5. By exchanging a cover flange 1 3 and the cover 10 together with the valve unit, it is possible to turn the pump on its side so that it can operate with a horizontal flow path, the valve again being vertical.

Fig. 4 shows how the connecting channel 4 between the suction inlet 2 and the pressure outlet 3 of a rotary piston pump 1 together with the pressure relief valve 7a, forms a separate duct screwed onto the rotary piston pump.

Claims

1. A pressure relief valve in a rotary piston pump which is arranged between the suction inlet and the pressure outlet of a pump stage and which opens if the pressure difference exceeds a maximum permitted value, wherein the valve is positioned vertically and is damped by one or more rectangular piston rings on a cylindrical piston within a cylinder sleeve, said value being determined by the weight of the piston, the rings and any weights placed on the piston.

2. A pressure relief valve according to claim 1, wherein the cylinder sleeve is formed by the housing of the valve and is closed by a cover.

3. A pressure relief valve according to claim 1 or 2 which is integrated in the side wall of a rotary piston pump (1).

4. A pressure relief valve according to any preceding claim, arranged in a connecting channel between the suction inlet and the pressure outlet of the pump, and the connecting channel itself is arranged in the middle part of the pump housing.

5. An arrangement according to any preceding claim, wherein the piston can be housed in either of two positions mutually at right angles, enabling the pump to be run in either of two positions.

6. A pressure relief valve according to any preceding claim which is arranged in a connecting channel between the suction inlet and the pressure outlet, said connecting channel being formed in a separate structural member bolted onto the remainder of the pump housing.

7. A pressure relief valve substantially as herein described in the accompanying drawing.

8. A rotary piston pump including a pressure relief valve as claimed in any preceding claim.