GB2082733A

GB2082733A - Dump Actuated By Pass Valve

Info

Publication number: GB2082733A
Application number: GB8121587A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-07-21
Filing date: 1981-07-14
Publication date: 1982-03-10
Also published as: GB2082733B

Abstract

In a high pressure fluid jetting system where it is required to control the supply of output flow from a fixed displacement pump to a high pressure jetting nozzle 38, a dump actuated by pass valve 22 is provided, connected into the system at pump outlet 15, with a return line 21 to the header tank feeding the pump and a supply line 29 connected to an existing type of dump control valve 39. A check valve 34 is provided in the line between the dump control valve outlet 30 and the jetting nozzle. In the off- load condition pump output flow is by passed back to the header tank, at a low pressure. A pilot flow is maintained in the line 29 from by pass valve outlet to the dump control valve. Manual operation of the dump control valve results in the actuation of the by pass valve and full pump output flow being directed to the jetting nozzle. Release of the dump control valve trigger causes a reversal back to the off-load condition. <IMAGE>

Description

SPECIFICATION Dump Actuated By Pass Valve The invention constitutes an improved method for controlling the constant flow output of a positive displacement pump such as is generally used for high pressure water jetting purposes.

The nature of the improvement is such as to allow the pump output to be by passed back to tank under reduced load conditions without the requirement for water to remain locked in the operators supply line at high pressure, as is the case with most existing systems. The exceptions are known systems which employ electrically/pneumatically actuated devices to accomplish the required by pass action.

High Pressure Water Jetting is the term generally applied to the process whereby the constant flow output of a positive displacement water pump normally in the range 10-30 GPM is applied via a delivery hose, at high pressure normally in the range 5000-1 5000 PSI to a nozzle hole, or holes, of relatively small diameter, from which it then emerges at relatively high velocity and is applied to carry out a wide range of tasks. Control of the flow of water to the nozzle, by an operator who may or may not also be holding and directing the lance to which the nozzle is attached, is necessary to allow the process to be interrupted without the output of flow from the pump having to be stopped and restarted.

Other than the electrical/pneumatic systems previously mentioned the methods of operator control fall into one of two categories, these being 'dry shut-off' or 'dump control'. In the 'dry shutoff' system the operator control is a normally closed gun, trigger operated to open. In the closed condition pump output maintains pressure in the supply line to the gun, this pressure acting to open a by pass valve to allow the pump flow to be returned back to the supply tank. This by pass flow may take place at either full pressure or some reduced pressure, depending on the type of valve used, but in both cases the supply line to the gun must remain pressurised. In the 'dump control' system the operator controls a normally open valve, the inlet side of which is connected to the supply line between pump and nozzle and the outlet side normally discharges to atmosphere.

Pump output is therefore free to discharge through this normally open valve until such time as the valve is closed by the operator forcing full pump output to exit through the high pressure nozzle. To interrupt jetting the control is released and flow again discharges freely to 'dump' through the normally open valve.

The invention provides for the addition of a novel by pass valve, for use in conjunction with existing well known dump control valves, which will divert fldw back to the supply tank when the system is off load, eliminating dumping which under existing methods takes place directly from the manually operated dump control valve. The advantages of this modified method of operation are prevention of the waste of water, normally associated with dump control systems, together with general improvement of safety conditions in the operating area, and the elimination of severe pressure pulses imposed on the equipment by pressure operated by pass devices.

A typical system arrangement would be shown in Figure 1. Positive displacement pump 1 is driven by prime mover 2, obtaining water supply from header tank 3 via inlet line 4 and discharging via high pressure line 5 to the by pass valve 6.

Under normal off load conditions the by pass valve is arranged to direct most of the pump output flow back to header tank 3, via return line 7, with a relatively low pressure being developed in line 5 and a small pilot flow allowed to pass out through supply line 8, to pass freely through the Dump Gun 9, discharging through the dump barrel 12. Operation of the Trigger 10 causes the by pass valve 6 to actuate, diverting full pump output to the Dump Gun 9, from where it passes to the outlet nozzle 14, via delivery barrel 11 and the system is put onto full pressure load. Release of the trigger reverses this process and re-directs the pump output to return line 7 and back to the header tank 3.

The novel features by means of which the above process takes place are shown in Figure 2 and may be described as follows: Under normal off load conditions the full water flow from the pump enters the by pass valve 6 at port 1 5. The piston 22, under the influence of spring 28 is positioned at the far left of its travel thus leaving a water flow path to chamber 26 where pressure applied to valve 19, against the influence of spring 20 lifts this valve from its seat 18 and allows water to exit through port 21 at return line pressure. The pressure developed in order to lift valve 1 9 applies to orifice 1 6 in the valve body, allowing a relatively small flow to pass into chamber 23 and thence to outlet port 1 7. This relatively small pilot flow then passes to the Dump Control Valve 9, via port 29.The Dump Control Valve is a weil known type of equipment of which a typical example is shown here to illustrate the method of operation. In the off load condition the pilot flow is allowed to exit freely through port 31.

To bring the system onto load trigger 10 of the Dump Control Valve 9 is operated. This causes piston 39 to be pushed inwards, thus closing off port 31. The pilot flow is now contained in the supply line 8, against piston 34 acting on conjunction with valve seat 33 in check valve 13.

Since the line is being supplied from the higher pressure present in chamber 26 via orifice 1 6 the pressure in the line will continue to rise until it approaches this higher level. At some predetermined point, this pressure, acting on the area of piston 22 sealing on valve seat 24 will overcome the force exerted by spring 28 and the piston will move to the right. It will continue to move to the right under the influence of the pressure in chamber 26 now acting on the piston formed by sealing diameter 27 until piston 22 contacts seat 25, thus closing off the flow path through chamber 26 and port 21, and causing the full pump output to be diverted to chamber 23 and thence to outlet port 1 7.The effect of this flow diversion is to cause piston 34 to lift from its seat 33 in check valve 13, allowing full flow to pass to orifice 38 in nozzle 1 4 and resulting in full load pressure being developed in order to maintain flow rate through the orifice. This full load pressure is applied on piston 34 via sealing diameter 36 to prevent any leakage through clearance diameter 37. The system is now on load and jetting may be carried out.

To interrupt jetting the trigger 10 is released, whereupon piston 39 moves outwards under pressure, allowing port 31 to open and flow to pass freely to dump. At the same time pressure at port 32 in check valve 13 drops to zero, allowing piston 34 to close back onto seat 33; also pressure at port 17 in by pass valve 6 drops to a level sufficient only to allow pump flow to be maintained through control valve 9, discharging through port 31 and dump barrel 12, as a transient condition. The system is arranged in such a way that this pressure at port 17, acting on piston 22 against seat 25 results in a force which is no longer sufficient to overcome the influence of spring 28 and the piston 22 now moves to the left, thus re-opening the path to chamber 26 and by pass port 21. The movement continues until the piston is back on seat 24, thus also closing off the main flow path to port 1 7. The system is now off load, with pump flow being returned to tank 3 via the by pass port 21 at a low recirculating pressure, with only the small pilot flow passing through the orifice 16, and via outlet port 1 7 to discharge freely through Dump Control Valve 9.

Claims

1. In a high pressure fluid pump system where the medium is normally but not exclusively water and where means are to be provided to control the flow of fluid to an outlet nozzle whilst delivery from the pump is maintained at a substantially constant rate, the provision of a means of diverting the major part of the pump flow back to the supply tank whilst maintaining only a low pressure load on the pump outlet, this by pass means being maintained without significant fluid pressure in the line connecting the by pass means to the outlet nozzle; and further, by using secondary means to cause pressure to increase in the line connecting the by pass means to the nozzle, to cause the by pass means to cease by passing and divert full pump flow into the line connected to the outlet nozzle.Conversely by using secondary means to cause pressure to decrease in the line connecting the by pass means to the nozzle to cause the by pass means to open and divert majority of pump clow back to the supply tank. Control throughout the operation being effected by the application of pump fluid pressure and flow only, without the additional use of electrical or pneumatic control elements.

2. In a system such as in claim 1 the by pass means being situated between the pump output and the secondary control means and remote from the secondary control means so that when in the by pass mode full pump flow is not passing through the secondary control means.

3. In a system such as in claim 1 the provision of a check valve means to prevent premature leakage of fluid from the line connecting the by pass valve to the nozzle, through the nozzle, until such time as the pressure in this line has reached a level sufficient to cause the by pass means to close, diverting full pump outlet flow into the line and thence to the nozzle.

4. In a system such as in claim 1 the by pass means to include in the by pass line a pressure control means in order to ensure that pressure is maintained in the valve at some predetermined level and flow is released via this pressure control means to by pass back to the header tank, at return line pressure.

5. In a system such as in claim 1 the by pass means to include an orifice which meters flow from that region of the valve which is held at a pre-determined pressure level when by passing takes place into the line connecting the by pass means to the secondary control means, and thence to the nozzle, to provide the means of pilot control.