GB1600363A

GB1600363A - Pump

Info

Publication number: GB1600363A
Application number: GB2740277A
Authority: GB
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1978-05-18
Filing date: 1978-05-18
Publication date: 1981-10-14

Description

(54) PUMP (71) We, IMPERIAL CHEMICAL IN DUSTRIES LIMITED, Imperial Chemical House, Millbank, London SW1P 3JF a British Company 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 performed, to be particularly described in and by the following statement: The present invention relates to a pump, in particular to a single action reciprocating pump.

Single action reciprocating pumps are widely used for small scale pumping in the chemical industry, e.g. in the manufacture of fine chemicals and in chemical and chemical engineering research. Although such pumps have proved satisfactory for a large number of applications we have found that when pumping a liquid which is held at less than atmospheric pressure the pump is unreliable and tends to "vapour lock" after a brief period of operation. The reason for the "vapour lock" is shown diagrammatically in Figure 1 attached to this specification.

Referring to Figure 1(a), 1 is a piston which is capable of reciprocating in a cylinder 2 which is provided with suction and delivery orifices 3 and 4 in which are located non-return valves 5 and 6 respectively.

Valve 5 is designed to open when the pressure P in the cylinder is less than pressure P2 in 3 and valve 6 is designed to open when P is greater than the pressure P1 in 4. In Figure 1(a) the piston is at the end of its delivery stroke and P is greater than both P1 and P so opening 6 and closing 5. In Figure 1(b) the piston is starting its suction stroke but P is not yet sufficiently low for P2 to exceed P so 5 remains closed and yet P is no longer sufficiently greater than P' to maintain 6 open. Both non-return valves are therefore closed. Figure 1 (c) shows the piston at the end of the suction stroke when P is at its minimum so that P2 iS greater than P and 5 is open while 6 remains closed.The problem of "vapour lock" is illustrated in Figure 1(d) which shows the increase in pressure in the cylinder as a result of vapourisation from the liquid being pumped combined with ingress of air through the pump glands which form a cushion of gas in front of the piston in the cylinder so increasing the pressure P to such an extent that it is not sufficiently less than P2 for 5 to open. As a consequence the pump loses suction. Although it is possible to deal with the ingress of air by known means e.g. a vented lantern ring this still leaves the problem of vaporisation from the liquid being pumped and in order to overcome this defect and so provide a pump which is particularly suitable for pumping liquids stored under reduced pressure we have designed a modified single action reciprocating pump.

According to the invention a single action reciprocating pump comprises (a) a cylinder provided with (i) suction and delivery ports, each port being equipped with a non-return valve and, (ii) a vapour exit port and (b) a piston adapted to reciprocate in the cylinder, the piston comprising a passage so formed as to connect the pumping chamber formed during the suction stroke with the vapour exit port via a lens ring or a circumferential groove in the piston when the piston is engaged in its suction stroke.

In this context "pumping chamber" means the space in the cylinder between the piston head and the suction and delivery ports which is created when the piston withdraws on its suction stroke.

The suction and delivery ports may be located in positions conventional for single actions reciprocating pumps e.g. diametrically opposite one another at one end of the cylinder. Both ports are provided with non-return valves so that the delivery port is closed when the suction port is open and vice versa.

Suitably the connection of the passage with the exit port takes place substantially at the end of the suction stroke. For example, the passage may run along the longitudinal axis of the piston turning at right angles to terminate in a hole on the piston surface at a distance such that it is capable of communicating with the exit port at the desired position of the suction stroke. The hole in the piston exits in a circumferential groove in the piston or in a lens ring so as to provide circumferential communication between the passage in the piston and the exit port even when the piston is rotated in the cylinder. In a preferred form of the invention the piston is located in the cylinder through a packed gland, the lens ring forming a part of the packing.In this embodiment of the invention the close contact between the cylinder internal wall and the surface of the piston effectively prevents movement through the passage in the piston until the exit of the latter is in communication with the exit port in the cylinder.

The vapour exit port in the cylinder is adapted to be attached to a source of pressure lower than that in the cylinder during the suction stroke of the pump and is preferably the vapour space in the storage vessel from which the pump takes suction.

In this way the gas from the cylinder is vented to the storage vessel.

The invention will now be further described with reference to the following diagrams in which Figure 2 is a vertical section through the pump showing the piston, Figure 3 is a view of the piston showing the communicating passage and Figure 4 a diagrammatic representation of the pump in use.

In Figure 2 the pump comprises a solid body 8 enclosing a cylinder 9 in which a piston 10 is free to reciprocate. Suction and delivery ports 11 and 12 are provided with non-return valves 13 and 14 respectively.

The piston enters the cylinder through a gland 15 which consists of a number of O-rings 16 made of a resilient plastic. A nut 17 screwing into the top of the cylinder bears down on the O-rings enabling them to be compressed against the pump body and the surface of the piston. An exit port 18 in the pump body wall is located so that it is coincident via a lens ring 19 with the exit 21 of a communicating passage 20. This passage through the piston is shown in Figure 3.

In operation, withdrawal of the piston in the cylinder draws in liquid through 11, valve 13 being open and valve 14 closed. At the end of the suction stroke the passage 20 comes into communication with exit port 18 and any gas in the cylinder is vented through 18. On the delivery stroke of the piston the exit 21 from the passage 20 is sealed by the cylinder wall so preventing movement of liquid through the passage while at the same time valve 13 closes and valve I4 opens enabling liquid to be delivered through 12.

In Figure 4 the liquid which is to be pumped is held in storage vessel 23 maintained under reduced pressure by pump 24 joined to the vessel through cold trap 25. A pressure gauge 26 and vacuum controller 27 complete the low pressure system. The pump 29 is as described in Figures 2 and 3 the outlet 18 being connected by line 28 to the storage vessel 23.

The pump takes suction from 23 through 11 and delivers through 12. On the suction stroke of the pump 21 comes into communication with 18 and vapour is vented via 28 to the storage vessel 23.

WHAT WE CLAIM IS: 1. A single action reciprocating pump which comprises (a) a cylinder provided with (i) suction and delivery ports, each port being equipped with a non-return valve, and (ii) a vapour exit port and (b) a piston adapted to reciprocate in the cylinder, the piston comprising a passage so formed at to connect the pumping chamber formed during the suction stroke with the vapour exit port via a lens ring or a circumferential groove in the piston when the piston is engaged in its suction stroke.

2. A single action reciprocating pump substantially as described in Figures 2 and 3.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. closed when the suction port is open and vice versa. Suitably the connection of the passage with the exit port takes place substantially at the end of the suction stroke. For example, the passage may run along the longitudinal axis of the piston turning at right angles to terminate in a hole on the piston surface at a distance such that it is capable of communicating with the exit port at the desired position of the suction stroke. The hole in the piston exits in a circumferential groove in the piston or in a lens ring so as to provide circumferential communication between the passage in the piston and the exit port even when the piston is rotated in the cylinder. In a preferred form of the invention the piston is located in the cylinder through a packed gland, the lens ring forming a part of the packing.In this embodiment of the invention the close contact between the cylinder internal wall and the surface of the piston effectively prevents movement through the passage in the piston until the exit of the latter is in communication with the exit port in the cylinder. The vapour exit port in the cylinder is adapted to be attached to a source of pressure lower than that in the cylinder during the suction stroke of the pump and is preferably the vapour space in the storage vessel from which the pump takes suction. In this way the gas from the cylinder is vented to the storage vessel. The invention will now be further described with reference to the following diagrams in which Figure 2 is a vertical section through the pump showing the piston, Figure 3 is a view of the piston showing the communicating passage and Figure 4 a diagrammatic representation of the pump in use. In Figure 2 the pump comprises a solid body 8 enclosing a cylinder 9 in which a piston 10 is free to reciprocate. Suction and delivery ports 11 and 12 are provided with non-return valves 13 and 14 respectively. The piston enters the cylinder through a gland 15 which consists of a number of O-rings 16 made of a resilient plastic. A nut 17 screwing into the top of the cylinder bears down on the O-rings enabling them to be compressed against the pump body and the surface of the piston. An exit port 18 in the pump body wall is located so that it is coincident via a lens ring 19 with the exit 21 of a communicating passage 20. This passage through the piston is shown in Figure 3. In operation, withdrawal of the piston in the cylinder draws in liquid through 11, valve 13 being open and valve 14 closed. At the end of the suction stroke the passage 20 comes into communication with exit port 18 and any gas in the cylinder is vented through 18. On the delivery stroke of the piston the exit 21 from the passage 20 is sealed by the cylinder wall so preventing movement of liquid through the passage while at the same time valve 13 closes and valve I4 opens enabling liquid to be delivered through 12. In Figure 4 the liquid which is to be pumped is held in storage vessel 23 maintained under reduced pressure by pump 24 joined to the vessel through cold trap 25. A pressure gauge 26 and vacuum controller 27 complete the low pressure system. The pump 29 is as described in Figures 2 and 3 the outlet 18 being connected by line 28 to the storage vessel 23. The pump takes suction from 23 through 11 and delivers through 12. On the suction stroke of the pump 21 comes into communication with 18 and vapour is vented via 28 to the storage vessel 23. WHAT WE CLAIM IS:

1. A single action reciprocating pump which comprises (a) a cylinder provided with (i) suction and delivery ports, each port being equipped with a non-return valve, and (ii) a vapour exit port and (b) a piston adapted to reciprocate in the cylinder, the piston comprising a passage so formed at to connect the pumping chamber formed during the suction stroke with the vapour exit port via a lens ring or a circumferential groove in the piston when the piston is engaged in its suction stroke.

2. A single action reciprocating pump substantially as described in Figures 2 and

3.