GB2138888A

GB2138888A - Priming valve and priming circuit for impeller pumps

Info

Publication number: GB2138888A
Application number: GB08303967A
Authority: GB
Inventors: Stephen Walker Tebby
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-02-14
Filing date: 1983-02-14
Publication date: 1984-10-31
Also published as: GB2138888B; GB8303967D0

Abstract

Passageway 1 connects the outlet side of an impeller pump to the valve body 2 which is then connected via passageway 3 to an air evacuating device. Valve rod 4 carries valve disc 5 which is biassed open by spring 8 to provide an open passageway during the priming process when the transported fluid is air but which closes on completion of the priming process when the transported fluid is water or a liquid. Pump outlet pressure maintains the priming valve in the closed position until such time as the impeller pump either stops pumping or loses its prime. <IMAGE>

Description

SPECIFICATION Improvements to priming valve and priming circuit for self-priming of impeller pumps This invention relates to the self-priming of general duty impeller pumps, including impeller pumps for fire fighting purposes.

Self-priming systems for general duty impeller pumps including impeller pumps for fire fighting purposes generally consist of an air pumping device which is arranged to evacuate air from the suction side of the impeller pump via either a float chamber or a priming valve.

The purpose of the float chamber is to prevent any appreciable amount of primed liquid from entering the air pumping device and may also connect the inlet of the air pumping device to atmosphere when it is not priming in order to reduce its power consumption. For example, see POLLAK, F, "Pump Users' Handbook", second edition, published by Trade 8 Technical Press Ltd., ISBN 85461 0707, 1980, page 153.

An alternative system involves the use of a priming valve which when in the open position allows communication between the suction side of the impeller pump and the air pumping device. For example see "Pumping Manual", 6th edition, published by Trade s Technical Press Ltd., ISBN 85461 0812, 1979, page 100. A piston inside this valve is connected to the outlet side of the impeller pump. The valve geometry is arranged so that the piston will close the passageway between the suction side of the impeller pump and the air pumping device when the outlet head of the impeller pump reaches a certain pressure.

This is the point at which the impeller pump is considered to be primed.

In many pumping configurations consisting of an impeller pump and an air pumping device for self-priming, the air pumping device is driven from a point remote from the suction side of the impeller pump. Consequently, the configuration contains lengthy and cumbersome passageways or pipework.

For example see MARTLEW, G.K., "Fire Engines", Proc Instn Mech Engrs 1967-68, Vol 182 Pt 2A, No. 7, and page 100 of "Pumping Manual" referred to above.

An additional feature characterizing selfpriming systems as described is that the air is primed from the suction side of the impeller pump. When priming is being carried out, the impeller pump delivery valves are frequently shut off to maintain suction. The priming process then consists of 2 phases. In the first phase, the air evactuated from the impeller pump suction pipe by the air pumping device is replaced by primed liquid up to a level corresponding to the top of the impeller eye in the impeller pump. The second phase of prime is accomplished at a much lower rate because air has to be expelled from, firstly, the space in the outlet volute which surrounds the impeller periphery and is above the level corresponding to the top of the impeller eye and, secondly, from the remote closed volumes of theimpeller pump diffuser and discharge manifolds.

In accordance with the present invention, the priming duct or passageway is connected to the outlet side of the impeller pump preferably at the highest available position in the outlet side of the impeller pump. The priming duct or passagway is then connected to a priming valve and this priming valve is connected to the air pumping device. The construction of the priming valve is such that it remains open when the transported fluid through it is air or a gas but closes when the fluid is water or a liquid.

In a multi-stage impeller pump, the present invention provides for the priming duct or passageway to be connected to the outlet side of any of the stages but especially to the outlet side of the first stage of a two stage or multi-stage pump used for fire fighting duty where a shut off valve is used to isolate the first stage from further stages as in U.K.

Patent 1234587.

The configuration thus described is therefore more compact than priming valves and priming circuits generally available and, additionally, the second phase of priming is more positive and is achieved more quickly than in existing systems because the air is evacuated directly from the remote closed volumes of the impeller pump.

One example of a priming valve and priming circuit assembly constructed in accordance with the invention is illustrated diagrammatically in the accompanying drawing, Fig. 1.

Passageway 1 connects the outlet side of the impeller pump not shown to the valve body 2.

Passageway 3 connects the valve body 2 with the air pumping device not shown. Valve rod 4 consists of valve disc 5 complete with sealing seat 6, and spring guide 7. The spring 8 produces an axial load on the valve rod 4.

In a modification not shown the valve rod 4, valve disc 5 and spring guide 7 are combined to form a valve sleeve or piston such as is found in a conventional relief or check valve. However in this modification the spring force acts in the opposite direction to the spring force normally contained in a conventional relief or check valve and the fluid is transported through the valve in a direction opposite to the direction normally associated in a conventional relief or check valve.

When the impeller pump is at rest, the priming valve rod assumes the position as shown in Fig. 1. Upon actuation of the air pumping device the priming process commences and air is drawn through the priming valve. This air flow produces an axial load on the valve rod 4 which is due to the air momentum thrust on the face of the valve disc plus the thrust created by the pressure difference across the valve. By arranging the spring load on the valve rod to exceed the sum of the two thrust components, the priming valve remains in the open position as illustrated in Fig. 1.

When the air pumping device has primed the impeller pump and water begins to be pumped through the priming valve, the axial load on the valve rod increases on account of both an increased volumetric throughput and an increased fluid momentum thrust. It will be appreciated that the momentum thrust will be substantially increased owing to the differences in specific gravity of air and water. The geometry of the priming valve is arranged so that the increased axial load on the valve rod is sufficient to close the priming valve against the spring force to a position shown in Fig. 2.

This is the point at which the impeller pump is considered to be primed.

The outlet pressure from the impeller pump is conveyed to the priming valve through passageway 1 and maintains the priming valve in the closed position until such time as the impeller pump either stops pumping or loses its prime.

It will be seen that a priming valve and priming circuit combination built in accordance with the present invention provides for a more positive and speedier prime and that this is achieved with a physically more compact arrangement.

Claims

1. A priming valve and priming circuit as herein defined to be provided between the outlet of an impeller pump and inlet of an air pumping device.

2. A priming valve assembly according to Claim 1 in which a valve body contains a closure member held open by a spring.

3. A priming valve according to Claim 1 and Claim 2 which is characterized in that it provides an open fluid passageway between the impeller pump and air pumping device when the transported fluid through it is air or a gas, but which provides for closure of that fluid passageway when the fluid is water or a liquid.

4. A priming liquid and priming circuit substantially as described with reference to the accompanying drawings.