EP0519880A1

EP0519880A1 - Inlet shut-off valve for rotary piston vacuum pump

Info

Publication number: EP0519880A1
Application number: EP92830312A
Authority: EP
Inventors: Franco Grazzini
Original assignee: Galileo Vacuum Tec SpA
Current assignee: Galileo Vacuum Tec SpA
Priority date: 1991-06-17
Filing date: 1992-06-17
Publication date: 1992-12-23
Also published as: IT1246969B; ITFI910143A1; ITFI910143A0; KR930000838A; JPH0681787A

Abstract

Rotary vacuum pump with a pressurized hydraulic circuit for lubrication and with a shut-off valve (15) for isolation between the vacuum environment (A) and the vacuum pump (1) when the pump is stopped; as a result of this stoppage and of the consequent pressure drop in the hydraulic circuit (29), an actuator (27) with a cylinder and piston (31, 33) is brought into operation and acts on a shaft (17) to lower a radial arm (25) against the action of a spring (37) which tends to move the shut-off valve (15) to the closed position.

Description

The invention relates to a novel shut-off system for the isolation of the vacuum environment from the vacuum pump when the pump is stopped and during its stoppage. The principal object of the invention is to avoid the use of a fluid - such as air or other gas, or oil or other liquid - to control said shut-off system, with a number of advantages which will become obvious from a reading of the following text which lists the principal advantages.
The rotary vacuum pump is of the type with a hydraulic circuit and associated pumping mechanism for lubrication and for auxiliary controls and with a shut-off valve for isolation between the vacuum environment and the vacuum pump when the pump is stopped and as a result of the consequent pressure drop in said hydraulic circuit. According to the invention, the pump comprisesfor the closing of said shut-off valve - a mechanical transmission acted on by an elastic means to move the shut-off valve to the closed position and an actuator operated by the pressure of the hydraulic circuit to cause the shut-off valve to move to the open position.
The mechanical transmission may comprise oscillating mechanisms with rocker arms or equivalent, but preferably it comprises a rotating shaft which passes through a wall separating the vacuum environment of the pump from the exterior, this shaft being combined with means of sealing in the form of a ring or similar.
Means of delaying the enabling of the movement of the shut-off valve to the open position, with respect to the starting of the pumping mechanism of the hydraulic circuit, are advantageously provided to ensure that a vacuum is produced within the pump before communication with the vacuum environment is re-established.
The invention will be better understood by following the description and the attached drawing, which shows a practical non-restrictive illustration of the invention. In the drawing,

Fig. 1 shows a partial longitudinal section of the pump with the shut-off valve in the open position;
Fig. 2 is a schematic plan view of the same;
Fig. 3 is an enlarged detail of Fig. 2; and
Figs. 4 and 5 show a section taken transversely with respect to the section in Fig. 1, on two planes, to illustrate the shut-off valve in the open and closed positions respectively.

In the illustrations in the attached drawing, 1 indicates the body of the pump as a whole, of which 3 indicates the rotor which is eccentric with respect to the cavity in which it operates; the body of the pump is immersed in the oil contained in the casing. The upper part of the casing and the free surface of the oil form a space indicated as a whole, by 5, where the discharge of the pump valves and of the various apertures of the hydraulic circuit takes place. The hydraulic circuit comprises its own pumping mechanism associated with the rotor of the pump. The environment 5 is at atmospheric pressure or in any case at a pressure greater than that of the cavity in which the vacuum pump causes a depressurization to limits which may in comparison be very extreme. 7 indicates the flange for suction and for coupling to the vacuum environment A with which the pump is associated. 9 indicates as a whole the vacuum environment formed in the body of the pump. In this environment a housing 11, vertical and coaxial with the coupling 7, is formed for a sliding rod 13 connected in an articulated way at its top to the shut-off valve 15 in plate form which can act against the seat 7A formed in the coupling 7. The shut-off valve 15 must be rapidly moved to the closed position against the seat 7A as soon as the vacuum pump has ceased to operate, in order to avoid a reduction of the vacuum in the environment connected to the coupling 7; the shut-off valve 15 must be capable of opening from the closed position against the seat 7A only when, as the operation of the pump is restarted, a sufficient level of vacuum has been recreated in the environment 9 to prevent disturbances in the level of vacuum of the environment to which the coupling 7 is connected; in practice, the shut-off valve 15 may be opened by gravity with the sliding of the guide rod 13 in the housing 11.
According to the invention, a control system is provided for the shut-off valve 15, in particular for its closing against the seat 7A, which does not make use of a control fluid which can cause the release of gas into the vacuum environment where this fluid might enter in the shut-off valve control operation; this occurs in a certain number of known solutions, which make use of control by air or other gas or by a liquid such as the oil used for the hydraulic lubrication circuit.
According the invention and according to the drawing, the closing is caused by a mechanical transmission which comprises a shaft 17 passing through a wall 1X of the pump, which separates the vacuum environment 9 from the environment 5 at atmospheric or equivalent pressure. The shaft 17 is accommodated in a component 19 which forms an extended journal bearing for the shaft 17 and also forms a housing for means of sealing - which may be multiple - to provide a seal around the shaft 17 which can rotate, in order to prevent a penetration of gas into the interior of the pump, in other words from the compartment 5 into the compartment 9; these sealing means may advantageously consist, for example, of a pair of ring seals known as O-rings, indicated generally by 21 and disposed in an environment which may for example contain grease or other equivalent sealing substance. This sealing system is reliable and permits easy rotary movements of the shaft 17. Within the compartment 9, the shaft 17 has a head 23 secured to it by a key or other system; said head has a radial arm 25 which extends into a longitudinal housing 13A in the rod 13; this housing is extended substantially in the form of a slot and may also be open at the lower end, in other words extended to the lower end of the rod 13; in all cases, the end of the arm 25 is capable of acting on the end of the longitudinal slot-shaped housing 13A. The shaft 17 extends into the compartment 5 and in this compartment has an elbow 17A and an extension 17B parallel to the shaft 17. In the body 1, under said extension 17B, there is an actuator indicated as a whole by 27, which is propelled by the lubricating liquid of the hydraulic circuit referred to previously; this circuit includes ducts such as the duct 29, which communicates with a cylinder 31 formed in the body 1 under the extension 17B of the shaft 17. In the cylinder 31 there slides a piston 33 which forms, with the cylinder 31, the said actuator 27 which is capable of acting on the extension 17B of the shaft 17 when the hydraulic circuit - of which the duct 29 and the cylinder 31 form part - is pressurized by the activation of the pump, in other words of the rotor 3 and the pumping mechanism of the hydraulic circuit. A valve with a ball 35, capable of blocking an aperture which opens to the environment 5 in a generally upward direction, is formed within the piston 33.
The shaft 17 is surrounded by a coil spring 37 which acts between the elbow 17A and a fixed support in such a way as to impart an angular force to the shaft 17 in the direction of the arrow fC which corresponds to the upward displacement of the arm 25, which causes a closing force to be applied to the shut-off valve 15, which is pushed elastically by the arm 25 via the cylindrical rod 13 against the seat 7A. The actuator 27 in turn is capable, under the internal pressure of the hydraulic circuit, of lifting the extension 17B causing the rotation of the shaft 17 in the opposite direction to fC and consequently the lowering of the arm 25, consequently also causing a lowering of the shut-off valve 15, a lowering which may be obtained as a result of the valve's own weight.
When the pump is inoperative, there is no pressure in the hydraulic circuit, and consequently in the cylinder 31 the spring 37 causes the closing of the shut-off valve 15 against the seat 7A of the coupling 7. When the pump is started, a flow of oil is established into the hydraulic circuit and consequently into the cylinder 31, the valve 35 is moved to the closed position by the flow, after which the pressure begins to rise in the circuit, and with a limited delay the piston 33 is raised as a result of the pressure and the shaft 17 is made to rotate in the opposite direction to the arrow fC against the action and by overcoming the action of the spring 37 until it lowers the arm 25 in an angular way along the longitudinal slot-shaped housing 13A. Consequently, the shut-off valve 15 is no longer pushed against the seat 7A by the elastic action of the spring 37 through the mechanical transmission which comprises the shaft 17 and the arm 25, and the shut-off valve 15 tends to be lowered under its own weight and that of its guide rod 13. Owing to the limited delay, this takes place as soon as the vacuum pump - which has started to rotate - has created a sufficiently high level of vacuum in the environment 9, in practice very close to the level of vacuum which can be achieved in the environment connected to the coupling 7, as a result of which the opening of the shut-off valve takes place without disturbance in the level of vacuum maintained in the environment A connected to the coupling 7. It is thus possible to start and stop the pump without the occurrence of appreciable fluctuations in the level of vacuum in the vacuum environment A previously created by the pump.
When the operation of the pump is stopped, and therefore when the pressure in the hydraulic circuit and consequently in the cylinder 31 is reduced, the action of the spring 37 causes the lowering of the piston 33 and the raising of the arm 25, and consequently the closing of the shut-off valve 15.
When the operation of the pump, and therefore that of the pumping mechanism of the hydraulic circuit, is stopped, the depressurization of the hydraulic circuit causes the valve 35 to open and allows air to enter through the oil outlet of the hydraulic circuit when this is required.
It will be noted that the action of the spring 37 closes the shut-off valve 15 even when the pump is dismounted from the user installation, thus preventing the possible penetration of foreign bodies into the environment 9 and consequently into the interior of the pump.
The arrangement described offers numerous advantages over the present solutions which operate with a fluid which constitutes the closing actuator.
The described closing system offers the following advantages, among others:

1) Exclusively mechanical control of the shut-off valve, without penetration of a hydraulic fluid - such as air (or other gas) or oil (or other liquid) into the vacuum environment 9.
2) Closing of the suction duct even when the pump is stopped or dismounted, so that the entry of contaminants from the environment and the exit of oil from the pump is prevented.
3) Absence of any kind of contamination of the suction duct by fluids (air and/or oil) used - in other known solutions - for the actuation of the shut-off valve.
4) Owing to the absence of the said contamination, there is no degassing of the fluids on starting, so that the attainment of a vacuum is very rapid on starting.
5) Complete absence of a rise in pressure on stopping, since the re-entry of air takes place after the mechanical device has caused the non-return shut-off valve 15 to close against the seat 7A.
6) Complete absence of a rise in pressure on starting, owing to the delayed opening system, which enables the shut-off valve 15 to descend only when the pressure in chamber 9 is sufficiently low.
7) Movement of the actuator 27 in a positive way by the oil pressure; this ensures ample margins of power for opening and closing.

It is to be understood that the drawing shows only an illustration provided solely as a practical demonstration of the invention, this invention being capable of being modified in its forms and arrangements without thereby departing from the scope of the guiding concept of the invention. The presence of any reference numbers in the attached claims has the purpose of facilitating the reading of the claims with reference to the description and to the drawing, and does not restrict the scope of protection represented by the claims.

Claims

A rotary vacuum pump with a hydraulic circuit and associated pumping mechanism for lubrication and for auxiliary controls and with a shut-off valve for isolation between the vacuum environment and the vacuum pump when the pump is stopped and as a result of the consequent pressure drop in said hydraulic circuit, comprising - for the closing of said shut-off valve (15) - a mechanical transmission (17; 25, 17A), acted on by an elastic means (37) to move the shut-off valve (15) to the closed position and an actuator (27) operated by the pressure of the hydraulic circuit (29, 31) to cause the shut-off valve (15) to move to the open position.
The rotary pump as claimed in the preceding claim, wherein the mechanical transmission comprises a rotating shaft (17) which passes through a wall (1X) separating the vacuum environment (9) of the pump from the exterior (5), this shaft (17) being combined with means of sealing (21).
The rotary pump as claimed in claim 1 or 2, wherein an arm (25) sliding along a longitudinal slotshaped housing (13A) formed in the guide shank (13) of the shut-off valve (15) is provided to control the closing of the shut-off valve (15).
The rotary pump as claimed in claim 1 or 2, wherein said shaft (17) has within the vacuum environment a radial arm or a rocker arm (25) or an equivalent member, capable of pushing the shut-off valve into the closed position, and a spring (37) impels said shaft (17) toward the closed position of the shut-off valve.
The rotary pump as claimed in preceding claims, wherein said spring (37) is a coil spring.
The rotary pump as claimed in preceding claims, wherein the actuator (27) comprises means of creating a delay in the enabling of the movement of the shut-off valve to the open position with respect to the starting of the pumping mechanism of the hydraulic circuit.
The rotary pump as claimed in claims 1 through 5, wherein the actuator (27) comprises a cylinder-and-piston system (31, 33) capable of acting on an elbow (17A; 17B) of said shaft (17), to cause it to rotate in a direction opposite that of the elastic force.
The rotary pump as claimed in preceding claims, wherein a valve (35) opening spontaneously under the effect of gravity is formed in said piston (33), and the closing time of said valve as a result of hydraulic pressure generates a delay in the enabling of the movement of the shut-off valve to the open position; said valve (35) also allowing the entry of air into the hydraulic circuit at the time of stopping.
The rotary pump with an automatically controlled shut-off valve for the isolation of the vacuum environment, the whole as described above and represented for illustrative purposes in the attached drawing.