GB2206673A

GB2206673A - Drain valve assembly

Info

Publication number: GB2206673A
Application number: GB08716096A
Authority: GB
Inventors: Colin Thomas Billiet; Robert Michael Fielding
Original assignee: Domnick Hunter Filters Ltd
Current assignee: Domnick Hunter Ltd
Priority date: 1987-07-08
Filing date: 1987-07-08
Publication date: 1989-01-11
Anticipated expiration: 2007-07-08
Also published as: GB8716096D0; GB2206673B

Abstract

In a drain valve assembly comprising a housing defining a drain inlet (7), and a discharge outlet (9) and wherein biasing means (19) bias a valve member (11) to a normally closed position seated on a valve seat (10) in which the valve member prevents flow from the drain inlet to the discharge outlet, an accumulator (21) receives a regulated flow of gas under pressure. Valve drive means (25, 16) are effective when the pressure in the accumulator reaches a given value to drive the valve member to an open position, so allowing drainage between the valve member and valve seat. Gas is exhausted from the accumulator when the valve member is in the open position, through an exhaust passage (31) that does not include the space between the valve member and valve seat. <IMAGE>

Description

DRAIN VALVE ASSEMBLY This invention relates to a drain valve assembly.

In the filtration of gas supplied from a compressor, the compressed gas flows through a filter system enclosed within a housing, the filter system acting, inter alia, to remove entrained liquid such as oil and water from the gas.

The liquid collects in a bowl section at the lower part of the housing and it must periodically be drained therefrom in order to maintain efficient flow through the filter.

There are, of course, other filter applications wherein liquid is removed from a gas stream and must be drained periodically from the filter assembly. Other items of equipment for example aftercoolers, driers, etc., also require periodic drainage from a housing.

There have been a number of proposals for valves capable of controlling drainage as aforesaid. The simplest is a manually operated valve, which is opened at intervals by an operator in order to allow drainage as required.

Automatic operation is, however, often preferred, and there have been various proposals for pilot valves capable of being opened in response to operation of a float responsive to the height of the liquid in the housing. When the liquid reaches a predetermined level, the float initiates drain valve opening in any one of a number of ways in order that draining may be effected. Construction of such float operated systems can be complex, and they tend to be unreliable, with particular difficulties being caused by sticking of the valve due to the presence of dirt and of sticky materials such as oil/water emulsions.

In order to obtain more positive operation it has also been proposed that drain valves be solenoid driven, being opened in response to an electrical signal applied at any suitable interval. Such systems have the disadvantage that they are costly and that they require a source of electrical power, which may not readily be available in the location of the valve. When used outdoors, or in hazardous environments, the electrical equipment must conform to all relevant regulations, thus often increasing its complexity and cost. Furthermore, solenoids are not particularly powerful, and if the valve sticks the solenoid may burn out or otherwise fail.

There is a need for a simpler and more reliable automatically operable drain valve assembly, and the object of the invention is to provide such an assembly.

According to the invention a drain valve assembly comprises a drain inlet, a discharge outlet, a valve member, valve biasing means biasing the valve member to a normally closed position seated on a valve seat wherein the valve member prevents flow from the drain inlet to the discharge outlet, an accumulator, means allowing a regulated flow of gas under pressure into the accumulator, valve drive means effective when the pressure in the accumulator reaches a given value to drive the valve member to an open position allowing drainage between the valve member and valve seat, and means allowing exhaust of gas from the accumulator when the valve member is in the open position, through an exhaust passage that does not include the space between the valve member and valve seat.

In operation, compressed gas flows into the accumulator over a given period until the pressure in the accumulator is sufficient to actuate the drive means, so opening the valve member. Drainage past the valve member takes place, and the valve member is held open during the period in which gas is exhausted from the accumulator until the pressure in the accumulator falls to a value at which the biasing means returns the valve member to its closed position. The valve member then remains closed through a further accumulation period, and the cycle is repeated so that the valve member is opened at intervals that are related to pressure build-up within the accumulator. It will be appreciated that the valve is entirely pressurecontrolled, without the need for any additional control by, for example, electrical, float or manual operation.

As filters and other devices fitted with drain valve assemblies in accordance with the invention will usually be used in a compressed gas line the gas supply to the accumulator can very readily be bled from that line, desirably on the downstream side of a filter so that clean, filtered gas is passed to the accumulator. The exhaust passage from the accumulator can then lead directly to the atmosphere, without fear of resultant atmospheric contamination. No separate gas supply is required in such cases, although such a supply could be provided if necessary.

Preferably the valve member has a valve stem terminating in a drive end that is spaced from the drive means when the valve member is in the closed position, and the drive means is driven when the pressure in the accumulator reaches the given value to impact against the drive end of the stem to drive the valve member to the open position. The liquids that are removed during filtration of a stream of contaminated gas are very often sticky, and will thus tend to hold the valve member onto the valve seat. By arranging for the drive means to impact with some force against the drive end of the valve stem a blow is imparted to the valve member on opening, which blow will overcome any tendency for the valve member to stick. This concept of impact is thus important whenever the valve is designed for use in an environment where sticking is liable to occur.

Preferably the assembly includes drive biasing means operative to bias the drive means away from the drive end of the valve stem. The pressure in the accumulator must therefore be sufficient to overcome the drive biasing means before the valve member can be opened. While there are many different arrangements that could be used to achieve this, it is preferred that the drive means carry a second valve member that closes an outlet from the accumulator until the pressure in the accumulator reaches the given value.

Desirably the drive means is in the form of a piston located within a cylinder, and the area of the second valve member exposed to pressure within the accumulator is less than the area of a closed end of the piston that is exposed to pressure within the accumulator when the outlet from the accumulator is opened. Thus, as soon as the second valve opens, the pressure in the accumulator is immediately applied to the much larger piston area, with the result that the piston is driven very rapidly against its biasing force and accordingly causes the required impact on the end of the valve stem.

The exhaust passage for gas from the accumulator can then conveniently be a bleed passage extending axially of the piston, to allow gas to bleed past or through the piston when the outlet from the accumulator is opened. The bleed passage may lead to an opening from the cylinder direct to atmosphere, or in other constructions to additional bleed passages in other components, which may eventually discharge to atmosphere or into the discharge outlet.

In order that the invention may be better understood specific embodiments of drain valve assemblies in accordance therewith will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a longitudinal section through a first embodiment of drain valve assembly; Fig. 2 shows a drain valve assembly generally similar to that of Fig. 1, fitted to the lower part of a filter housing; and Fig. 3 is a cross-section through a second embodiment of drain valve assembly fitted within a filter housing.

Referring to Fig. 1 there is shown a drain valve assembly comprising a housing having three sections, a centre section 1, a first end section 2 secured to the centre section by screw threads 3, and a second end section 4 secured to the centre section by screw threads 5. A sealing ring 6 is incorporated between the end section 4 and centre section 1.

The first end section 2 has an internally threaded drain inlet 7, which may be threaded onto a drain from the housing of a filter or other device. The inlet is formed at one end of a through bore, the other end 8 of which is also internally threaded in order to receive, for example, a plug. A discharge outlet 9 extends through the first end member transversely to the bore 7, 8, and is again internally threaded in order to receive a discharge line.

The discharge outlet is formed with an inwardly tapering valve seat 10 in the region of its intersection with the drain inlet 7, and a valve member 11 is co-operable with the valve seat 10. The valve member 11 is carried at one end of a valve stem 12 which extends through the drain inlet and through a central opening 13 in an end wall 14 of the first end section 2. A sealing ring 15 surrounds the valve stem where it passes through the opening 13.

The valve stem 12 terminates in an externally threaded end section 16 over which is fitted a spring retainer 17 held in position by a nut 18 screwed onto the threaded end 16. The spring retainer 17 holds a compression spring 19 captive between itself and an annular rim 20 formed on the end wall 14. The spring 19 serves to bias the valve member 11 into its closed position on the valve seat 10 as shown in Fig. 1.

The centre section 1 of the housing is shaped to form an accumulator chamber 21 and a cylinder 22. The cylinder is closed at one axial end by a wall 23 intermediate the chamber and the cylinder, and at the opposite axial end by the end wall 14 of the first end section 2. A piston 24 is located within the cylinder 22, the piston having a closed end 25 and a hollow body 26 into which the valve stem 12 projects. The closed end 25 carries a second valve member in the form of a resilient disc 27, which is biased into contact with a seat 28 by a second compression spring 29.

When so seated, the disc 27 closes a passage 29 leading from the chamber 21 to the cylinder 22.

The piston body 26 is such that it is a loose fit within the cylinder 22, so that a bleed passage is formed between the outer circumference of the piston and the inner circumference of the cylinder. The cylinder has an outlet 31 to atmosphere, in a location remote from the opening 29.

The accumulator chamber 21 may be applied with compressed air through an air line connected to an internally threaded opening 33 that communicates with the chamber by a restricted passage 34. The cross-section of the passage 34 is designed to allow a regulated flow of gas under pressure into the accumulator.

In operation, when used in conjunction with a filter in a compressed air line, the drain from a filter housing is connected to the drain inlet 7, the outlet 8 is plugged, a drain outlet is connected to the discharge 9 and a supply of compressed air is connected to the inlet 33. The air supply is desirably taken through a connecting line from the flow of air downstream from the filter. Air accumulates in the chamber 21 at a rate dependent on the air pressure and the cross-sectional area of the passage 34. While it is so accumulating, the spring 19 holds the valve member 11 on its seating in order to close the drain from the filter housing, and the spring 29 holds the valve disc 27 on its seat 28. When the pressure in the accumulator is sufficient to overcome the action of the spring 29, the valve disc 27 opens.The accumulator pressure is thus immediately applied to the full area of the closed end of the piston, rather than just the area of the valve disc 27, with the result that there is a very rapid increase in force on the piston, so driving the piston away from the accumulator and causing it to impact against the end 16 of the valve stem. This blow, as well as overcoming the force of the spring 19, also overcomes any adhesion between the valve member 11 and the valve seat 10 with the result that the valve member is positively and forcibly driven off its valve seat so opening communication from the drain inlet to the discharge outlet. Liquid thus drains from the filter housing.

Air under pressure bleeds from the accumulator between the piston 24 and the cylinder 22 and leaves the cylinder by way of the discharge opening 31. The cross-sectional area of the bleed passage around the piston is chosen to be greater than the cross-sectional area of the passage 34 so that the bleed rate from the accumulator is greater than the rate of replenishment to the accumulator. As the pressure in the accumulator falls, so the opening force on the piston 24 also falls and the combined effects of the springs 19 and 29 will, in time, return the parts to the positions shown in Fig. 1. The cycle can then recommence.

It will understood that the valve is responsive to gas pressure only, and the simplicity and effectiveness of its construction will be appreciated from the foregoing description.

Fig. 2 shows an assembly very similar to that shown in Fig. 1, and corresponding parts have been given the same reference numbers as used in Fig. 1. Fig. 2, however, shows the assembly actually connected to the lower part of a filter housing 40 and lying externally of that housing.

It also shows the lower exit channel 8 closed, not by a simple plug, but by a manually operable drain 41 that can bused as an alternative to the pressure-controlled drain if required. In this embodiment the gas pressure supply to the accumulator is by way of a manually controllable needle valve 42 in order that the rate of accumulation, and thus the frequency with which the drain is opened, may be regulated. The accumulator is also shown fitted with a second needle valve 43 controlling bleed directly from the accumulator to the atmosphere. By adjustment of the valve 43 the time required to reach the operating pressure can be controlled as desired.

Figs. 1 and 2 both show assemblies designed to be mounted externally of the filter housing. Fig. 3 shows an alternative embodiment designed for mounting within the lower part of the filter bowl. The assembly comprises a housing 50 having a lower flange 51 capable of being seated against the lower wall of the filter bowl, a spigot 52 projecting from the flange through an opening in the filter bowl. A nut 53 can be secured on an externally threaded part of the spigot in order to secure the assembly to the filter bowl, and a sealing ring 54 is located between the flange 51 and the bowl. The housing 50 has an internal wall 55 which is joined to the flange 51 by an annular section 56 through which a series of radially extending openings 57 are cut. The openings communicate with a chamber 58 connected by a passage 59 to the hollow interior of spigot 60, that interior forming a discharge outlet. A valve seat 61 is formed in the discharge outlet. Mounted within a cylinder section 62 of the chamber 50 is a piston 63, which is biased upwardly by a compression spring 64.

The piston has a hollow body and a valve stem 65 projects into that hollow body, the valve stem carrying a valve member 66 engagable with the valve seat 61. The valve member 66 is biased into contact with the seat by a further compression spring 67.

The piston carries a valve disc 68 which is biased by the spring 64 into engagement with a valve seat 69 surrounding an opening 70 in a wall of the housing 50. The housing 50 is surrounded by an outer housing 71, the space between the two housings forming an accumulator chamber.

An orifice 72 is formed in the outer housing 71 at the uppermost section thereof.

Operation of the assembly is analogous to that already desribed. As compressed gas flows through the filter the liquid removed from the gas falls into the filter bowl and collects in the bottom thereof, flowing through the openings 57 into the chamber 58 and being held by the valve 66. Part of the gas being filtered bleeds through the orifice 72 into the accumulation chamber, and eventually the pressure in the chamber will overcome the force of spring 64 so opening the valve 68. The pressure applied to the full area of the piston 62 will then forcibly drive that piston to strike the valve stem, so opening the valve and allowing liquid to drain. Compressed gas from the accumulator can bleed past the piston and be exhausted to atmosphere by way of a bleed passage 73 extending axially through part of the housing 50.

It will be appreciated that it is contaminated gas that bleeds from the accumulator, and if it is desired that this should not be discharged to atmosphere then the exhaust passage may be by way of a passage bored axially through the valve stem and opening into the discharge outlet 60.

It will be appreciated that modifications can be made to the assemblies particularly described, and that other configurations for the pressure operated drain valves of the invention are possible.

Claims

1. A drain valve assembly comprising a drain inlet, a discharge outlet, a valve member, valve biasing means biasing the valve member to a normally closed position seated on a valve seat wherein the valve member prevents flow from the drain inlet to the discharge outlet, an accumulator, means allowing a regulated flow of gas under pressure into the accumulator, valve drive means effective when the pressure in the accumulator reaches a given value to drive the valve member to an open position allowing drainage between the valve member and valve seat, and means allowing exhaust of gas from the accumulator when the valve member is in the open position, through an exhaust passage that does not include the space between the valve member and valve seat.

2. A drain valve assembly according to claim 1 in which the valve member has a valve stem terminating in a drive end that is spaced from the drive means when the valve member is in the closed position, and the drive means is driven when the pressure in the accumulator reaches the given value to impact against the drive end of the stem to drive the valve member to the open position.

3. A drain valve assembly according to claim 2 and including drive biasing means operative to bias the drive means away from the drive end of the valve stem.

4. A drain valve assembly according to claim 3 in which the drive means carries a second valve member that closes an outlet from the accumulator until the pressure in the accumulator reaches the given value.

5. A drain valve assembly according to claim 4 in which the drive means is in the form of a piston located within a cylinder, and the area of the second valve member exposed to pressure within the accumulator is less than the area of a closed end of the piston that is exposed to pressure within the accumulator when the outlet from the accumulator is opened.

6. A drain valve assembly according to claim 5 in which the piston has a hollow body and the valve stem projects into the hollow body and extends towards the closed end of the piston.

7. A drain valve assembly according to claim 5 or claim 6 in which the drive biasing means is a compression spring biasing the piston towards the accumulator and away from the drive end of the valve stem, and the valve biasing means is a further compression spring biasing the valve stem towards the closed end of the piston.

8. A drain valve assembly according to any one of claims 5 to 7 in which the exhaust passage for gas from the accumulator is a bleed passage extending axially of the piston to allow gas to bleed past or through the piston when the outlet from the accumulator is opened, the bleed passage leading to an opening from the cylinder.

9. A drain valve assembly substantially as herein described with reference to any one of the accompanying drawings.