GB2135023A

GB2135023A - Non-return valve

Info

Publication number: GB2135023A
Application number: GB08401136A
Authority: GB
Inventors: David John Cunningham Law
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1983-02-12
Filing date: 1984-01-17
Publication date: 1984-08-22
Also published as: GB8401136D0; GB2135023B

Abstract

A non-return valve of the ball type includes a port 12 which opens into a cylindrical chamber 11. A seating 13 is defined about the port and a ball valve member 14 is located in the chamber for sealing engagement with the seating. A stop 17 defines a stop surface 16 which limits the movement of the valve member away from the seating. The dimensions of the valve are such that when the valve member is lifted from the seating it is guided by the wall of the chamber and it contacts only the stop surface 16 and the wall of the chamber and the difference between the diameters of the valve member and chamber is such that valve member is urged positively into the seating by the flow of liquid from the chamber to the port. <IMAGE>

Description

SPECIFICATION Non-return valves This invention relates to ball type non-return valves of the kind comprising a body defining an annular seating about a port in the body, said port opening into a chamber and a ball valve member located in said chamber, said ball valve member being moved into sealing engagement with said seating to prevent flow of fluid from said chamber to said port but lifting from the seating to allow flow of fluid from the port to the chamber.

In order to improve the operation of the valve it is known to limit the lift of the valve member so that when fully open the valve member is still confined by the seating and the surface of the stop which is used to limit the lift of the valve member. It has been found that under certain conditions of operation particularly when a high pressure surge appears in the chamber, the valve member does not close in a reliable manner it having been observed that the valve member tends to take a spiral path around the seating and in some cases does not form an effective seal with the seating. It is known to provide aids such as springs and fluid pressure actuated pistons, to assist the movement of the valve member onto the seating but such aids add to the complexity of what otherwise is a simple valve.Moreover, especially in the case where springs are used the reliability of the valve over an extended period, may be impaired.

The object of the invention is to provide a ball return valve of the kind specified in a simple and convenient form.

According to the invention a ball return valve of the kind specified includes a stop to limit the extent of movement of the ball valve member away from the seating, the wall of said chamber defining a cylindrical guide surface, the diameter of said guide surface being slightly larger than the diameter of the ball valve member so as to increase the closing force acting upon the ball valve member in the direction to close the valve.

According to a further feature of the invention said stop has a stop surface disposed substantially at right angles to said cylindrical surface, the lift of the valve member being such that in moving away from the seating the ball valve member can engage only said stop surface and said cylindrical surface.

The invention will now be described with reference to the accompanying drawings in which: Figure 1 is a sectional side elevation of a known form of non-return valve; and Figure 2 is a view similar to Figure 1 showing a non-return valve in accordance with the invention.

Referring to the drawings the non-return valve includes a body 10 which defines a chamber 11. Opening into the chamber is a port 1 2 and surrounding the port is an annular truncated conical seating 1 3. For co-operation with the seating there is provided a ball valve member 14 and the extent of movement of the valve member away from the seating is determined by a stop surface 1 6 on a stop member 1 7 which may be formed on a part not shown, closing the open upper end of the chamber 11 or on a part which extends partly over the chamber. Flow of liquid for example fuel, into the chamber 11 from the port 1 2 will cause the ball valve to move away from the seating into contact with the stop.The wall of the chamber 11 does not constitute a guide surface and in the example shown in Fig. 1, will not be contacted by the ball valve member. The movement of the ball valve member in the direction away from the port, will of course be determined by the stop 1 6 but it may also maintain engagement with the seating 1 3. The seating 1 3 forms an acute angle with the stop surface 1 6 and it is possible for the ball valve member to become wedged between the seating and the stop surface and as a result when the fluid pressure in the chamber 11 increases the ball valve member may not necessarily return to its seating to establish sealing engagement therewith.As has been explained above, it has been observed that sometimes the ball valve member undertakes a spiral path of movement about the seating. In some instances the ball valve member never establishes sealing engagement with the seating.

Turning now to Fig. 2, the general dimensions of the various components with the exception of the chamber 11 are substantially the same. In Fig. 2 however it will be noted tha the diameter of the cylindrical surface forming the chamber 11 is very much reduced and in fact is only slightly larger than the diameter of the ball valve member 14.

The diameter of the chamber is indicated by the reference letter A and the diameter of the ball by the reference letter B. In this example when the ball valve member is lifted from the seating its movement is limited by the stop surface 1 6 but in this example the dimension A in relation to the dimension B is such that the ball valve member can only contact the stop surface 1 6 and the wall of the chamber 11. The stop surface 1 6 is disposed at right angles to the wall of the chamber 11 so that the possibility of the ball valve member becoming wedged as described above, is minimised.

The small differences between the dimensions A and B provides an annular clearance between the ball and the wall of the chamber and the pressure drop which occurs due to any fluid which may flow through this clearance, acts upon the ball valve member in the direction to close the ball valve member onto its seating. The pressure drop acts over the maximum cross sectional area of the ball valve member whereas in the known construction as shown in Fig. 1, such pressure drop as there is acts over the seat area only.

The dimensions of the valve shown in Fig.

2 and which give the improved performance over the valve shown in Fig. 1 can be chosen within the following ranges. For a ball valve member having a diameter of between 1.0 mm and 10.0 mm the difference between the dimensions A and B may be up to 10% of the diameter of the ball valve member. Preferably the difference should lie between 8% and 7% of the diameter of the ball valve member. The clearance between the ball valve member and the stop surface in the closed position of the valve member should lie between 5% and 3% of the diameter of the ball valve member. The included angle C of the seat may be up to 90 but preferably should lie between 65 and 55

Claims

1. A ball type non-return valve comprising a body defining an annular seating about a port in the body, said port opening into a chamber and a ball valve member in said chamber, the ball valve member being moved into sealing engagement with said seating to prevent flow of fluid from said chamber to said port but lifting from the seating to allow flow of fluid from the port to the chamber, a stop to limit the extent of movement of the ball valve member away from the seating, the wall of said chamber defining a cylindrical guide surface, the diameter of said guide surface being slightly larger than the diameter of the ball valve member so as to increase the closing force acting upon the ball valve member in the direction to close the valve.

2. A ball type non-return valve according to Claim 1 in which said stop has a stop surface disposed substantially at right angles to said cylindrical surface, the lift of the valve member being such that in moving away from the seating the ball valve member can engage only said stop surface and said cylindrical surface.

3. A ball type non-return valve according to Claim 2 in which for a ball valve member having a diameter of between 1.0 mm and 10.0 mm the difference between the diameter of the guide surface and the diameter of the ball valve member being between 7% and 8% of the diameter of the ball valve member and the stop surface in the closed position of the valve member being between 3% and 5% of the diameter of the ball valve member.

4. A ball type non-return valve according to Claim 3 in which the included angle of the seating lies between 55 and 65 .

5. A ball type non-return valve substantially as herein described with reference to Fig. 2 of the drawings.