GB2044406A

GB2044406A - Change-over valve

Info

Publication number: GB2044406A
Application number: GB8006584A
Authority: GB
Original assignee: Klein Schanzlin and Becker AG
Current assignee: Klein Schanzlin and Becker AG
Priority date: 1979-03-02
Filing date: 1980-02-27
Publication date: 1980-10-15
Also published as: DE2908165B1; AT363322B; IT1150086B; IT8020200A0; DE2908165C2; GB2044406B; FR2450397A1; FR2450397B1; ATA90880A

Abstract

The valve comprises a pivoted flap 2, mounted on a pin 3 for pivoting between a position engaging a seat at the end of passage 4 and a position engaging a seat at the end of passage 5, the passages 4 and 5 being connected in use to the outlets of respective independently operable centrifugal pumps, so that the valve member 2 pivots automatically to close off the outlet of whichever pump is stopped, and occupies a central position, opening both passages 4 and 5, if both pumps are operating. In order to damp the movement of the valve member onto these seats, a dash pot is provided comprising a cylinder pivotally connected at one end on a pivot 8 and a piston 10 pivotally connected with valve member 2 via a pin 12 extending through a longitudinal slot 11 in the wall of cylinder 9. The slot 11 stops short of the end portions of cylinder 9 into one of which the piston 10 enters towards the end of the movement of the valve member into engagement with either of the valve seats, so that the damping action is substantially confined to this region of the range of movement of the valve member. <IMAGE>

Description

SPECIFIGATION Change-over value This invention relates to a change-over valve suitable for a unit consisting of two independently operated centrifugal pumps.

Units are known which comprise two independently operable pumps having their outlets connected to a valve in which a valve member is so pivotally disposed in a chamber connecting the outlets of the two pumps as to be able to close automatically the outlet of the stationary pump while one of the pumps is operating and the other is stopped, and assume a central position freeing both outlets when both pumps are in operation.

The object of the change-over or selector valve disposed on the delivery side of a double pump unit is to prevent any return flow through whichever pump is stationary. When the operating pump is shut down and the stationary pump is started up, the valve member is lifted from the seat it occupied until then and, after a pivoting movement, is moved on to the other seat by the changing pressure conditions. Since this movement usually takes place very violently, if the valve is undamped the change of pumps is usually accompanied by a noisy impact resulting not only in noise nuisance transmitted through the connected pipe lines, but often also destruction of the valve.

Some damping of the change-over movement and of the valve impact has already been obtained by constructing a change-over valve in the form of a double valve comprising individual valve members movable independently of one another and pressed on to the pump outlet orifices by means of springs (German Patent Specification 1 5 28 649). It has, however, been found in practice and by noise measurements that this solution entails an intolerably high noise level, particularly in the case of large double pump units.

The change-over impacts can be appreciably reduced with the double valve only if a relatively stiff leaf spring is used. However, because, in such a double valve, whichever valve member is in the open position is held open by the fluid flow past it, in opposition to the spring force, during operation of the pump, the hydraulic resistance automatically also increases as the spring stiffness increases. This means that the pump output is reduced with the noise reduction.

In addition, the spring cannot be expected to have a long life because of the continual vibrations towhich it is subjected during operation.

The object of the. invention is to provide a change-over or selector valve of the kind indicated hereinbefore with a damping system such as to avoid the impacts on change-over and leave the pump outlet unaffected.

According to the invention there is provided a change-over valve for a unit consisting of two independently operated centrifugal pumps, the valve including a valve member so pivotally disposed in a chamber connecting the outlets of the two pumps as to close the outlet of the stationary pump while one of the pumps is in operation and assume a central position freeing both outlets when both pumps are in operation, characterised by a dash pot cylinder which is disposed pivotally with respect to the valve and which contains a piston slidable therein and connected for pivotal movement to the valve by means of a pin extending through an aperture in the wall of the cylinder, the length of the aperture in the wall of the cylinder being such that the piston does not enter a closed cylinder compartment until it reaches the end of each of the two possible pivoting movements.

Dash pots comprising a piston and cylinder and acting in consequence of the decelerated movement produced on displacement of a volume of fluid are known basically. They have hitherto been. used more particularly for non-return valves of all kinds. Apart from the use of an external fluid, such as oil, as the damping medium, the fluid being delivered has also been used for damping purposes, being fed into the cylinder via a conduit or slots (German Patent Specification 10 43 737).

The dash pot cylinders in the known constructions were always disposed fixedly outside the valve housing. They could therefore act only within the direction determined by the vertical or horizontal reciprocation of the piston rod. The damping or non-return valves required a lever system to interconnect the piston, valve and valve housing. Such damping systems, which are frequently complicated, were hitherto used only for valves of the kind co-operating with one seat.

They were not used for change-over or selector valves co-operating with two seats.

In some cases the known dash pots already have available lost-motion or similar means which break the operative connection between the dash pot and the non-return valve during part of the movement of the valve and thus allow undecelerated movement of the valve through a predetermined travel. For example, in one known system (German Patent Specification 647 978) the piston rod has a slot in which a pin connected to the non-return valve lever system is slidable.

In another known non-return valve having an assocjated dash pot, (German Patent Specification 852 323), the non-return valve and the dash pot are separated from one another by connecting the dash pot piston to a cam via a piston rod and a lever mounted in the valve housing, the non-return valve coming into contact with said cam towards the end of its closing movement.

The disadvantage of breaking the connection between the dash pot piston over a considerable distance and restoring it only towards the end of the closing mdvement is that engagement of the co-operating parts takes place with a violent impact if the valve is subjected to relatively high acceleration and part from noise nuisance this results in considerable wear, if not destruction, of the parts in question.

The preferred embodiment of change-over or selector valve according to the invention has a dash-pot which is effective without a lever system for connecting the dash pot piston and the valve member. It also works in two closing directions of the valve. Harmful impacts when the dash pot operates are avoided as a result of the permanent connection between the valve and the piston and the free wheel system specific to the invention.

An embodiment of the invention is described below with reference to the accompanying drawings, in which: Figure 1 is a partial view, in section on the line D-E in Figure 2, of a valve embodying the invention, and Figure 2 is a view in section on the line A-C in Figure 1.

Referring to the drawings, a change-over valve comprises a housing 1 affording a valve chamber accommodating a valve member 2, first and second passages 4 and 5 connected, in use of this embodiment, to the outlets of respective centrifugal pumps, and a third passage 6 connected to an outlet of the unit. The passages 4, 5 and 6 all communicate with said chamber, the passages 4 and 5 terminating in the chamber, in respective valve seats.

The valve member 2 is pivotally mounted in the housing 1 by means of a-pin 3. Valve member 2 can be pivoted between a position in which it engages the seat associated with passage 4 to close off passage 4 and a position in which it engages the seat associated with the passage 5, to close off passage 5. Housing 1 is closed by a cover 7 (Figure 2) which is secured by bolts (not shown).

A dash pot cylinder 9 pivotable at one end with respect to the housing about a pin 8 is disposed opposite the valve member 2. Slidable longitudinally within cylinder 9 is a piston 10 which is pivotally connected to the valve member 2 by means of a pin 12 passing through a longitudinal slot 11 in the wall of the cylinder 9.

The slot 11 stops short of either end of the cylinder 9 so that compartments closable by the piston 10 are formed at each end. It may, however, be possible to dispense with a closable end compartment portion at the end of cylinder 9 nearer pivot 8 retaining such a closable portion only at the other end.

The change-over valve and dash pot illustrated operate as follows: While the centrifugal pump delivering the outlet 4 is in operation and the other pump is stationary, valve member 2 remains in the position shown in the drawing, because of the pressure built up by the operating pump.

If the pump that has been in operation is then shut down and the hitherto stationary pump is started, the valve member 2 is lifted from its sea; associated with passage 4, pivoted about pin 3 and placed on the other seat as a result of the varying pressure conditions in the outlets 4 and 5 and in the housing 1. This operation takes place in a number of phases: On starting up of the pump delivering to outlet 5, the valve 2 is initially in the position in which that outlet is closed. The pressure building up in outlet 5 first has to overcome the resistance to movement of the valve member in the direction to open passage 5, which resistance arises as a result of the suction effect of the piston 10 in the closed end part of the cylinder 9.During this phase, the valve member 2 is moved slowly out of its end position, whilst fluid is drawn in through the annular gap between the piston and the cylinder wall by the negative pressure forming in the closed part of the cylinder 9. The valve 2 is thus lifted from its seat associated with passage 5 at a iow speed..

In the next phase, piston 10 fully enters the area of the aperture 11, so that the fluid displaced by piston 10 and entering the cylinder 9 behind piston 10 can flow through the aperture 11 which does not present appreciable resistance to such flow. The valve member 2 is thus moved at an accelerated rate in this phase.

The piston 10 is at its furthest distance from the closed end of cylinder 9 furthest from pivot 8 in the dead-centre position between pivots 8 and 3 and moves back towards said closed end during further movement of the valve-member 2 towards passage 4.

Towards the end of the change-over movement, the piston 10 ayain enters a closed part of the cylinder 9. As it continues to move, the piston 10 must displace the liquid in the part of the cylinder through the annular gap between the piston and the cylinder wall. The movement of the valve member is thus considerably retarded. The valve member 2 is thus damped in its movement into engagement with the seat of the outlet 4.

The change-over in the other direction takes place correspondingly. When both pumps are delivering, the valve 2 will assume a middle position in the manner conventional with changeover valves without a dash pot, the piston 10 being, in this condition, in the dead centre position.

The change-over valve described with reference to the drawings which uses the fluid under delivery as the damping medium, has substantial advantages: Since the piston 10 pivotally connected to the valve member does not enter the closed end part of the cylinder until the end of the pivoting movement, there is not only effective damping but also a generally fast change-over.

This is important particularly because when the pumps are changed over the pump which is stopping must not be driven against its direction of rotation by the delivery from the pump that has started up, since the mechanical seal might be damaged. The outlet port of the pump which is stopping is thus closed before the pump that is starting can deliver through the other pump housing.

As it passes along the region in which slot 11 is provided in the cylinder wall, the piston 10 displaces the fluid in the dash pot cylinder readily, without significant resistance. The piston and the valve member connected thereto can therefore move very rapidly. As the piston 10 enters the closed compartment towards the end of the pivoting movement, the fluid in this part of the cylinder is displaced solely through the annular gap between the piston and the cylinder wall. The resulting considerable deceleration is utilised to damp the movement of the valve on to the seat of the pump outlet.

Since the piston also moves in the closed part of the cylinder at the beginning of the change-over operation, so that the latter is introduced with a delay, the additional advantage is obtained that the pumps always start with the delivery spigot closed when they are started up.

Claims

1. A change-over valve for a unit consisting of two independently operated centrifugal pumps, the valve including a valve member so pivotallydisposed in a chamber connecting the outlets of the two pumps as to close the outlet of the stationary pump while one of the pumps is in operation and assume a central position freeing both outlets when both pumps are in operation, characterised by a dash pot cylinder which is disposed pivotally with respect to the valve and which contains a piston slidable therein and connected for pivotal movement to the valve by means of a pin extending through an aperture in the wall of the cylinder, the length of the aperture in the wall of the cylinder being such that the piston does not enter a closed cylinder compartment until it reaches the end of each of the two possible pivoting movements.

2. A change-over valve suitable for a unit consisting of two independently operated centrifugal pumps, the valve including a housing providing a valve chamber and a first, a second and a third passage extending to said valve chamber, said first and second passages terminating in valve seats in said valve chamber, and a valve member pivotally mounted in said valve chamber for movement between a position in which it engages one of said valve seats and is out of engagement with the other and a position in which it engages said other of said valve seats and is out of engagement with said one valve seat, through intermediate position in which it is out of engagement with both said valve seats, said valve being operable, when a respective centrifugai pump is connected with each of said first and second passages, to connect said third passage, via the valve chamber, with the pump which is in operation whilst cutting off from said third passage the pump which is not in operation, when only one of said pumps is in operation, and to connect said third passage with both said first and second passages with said valve member in said intermediate position, when both said pumps are in operation, said change-over valve means including a dash pot cylinder which is pivotally connected with the valve housing and which contains a piston slidable therein, said piston being pivotally connected with said valve member by means of a pin extending through a longitudinal slot in the wall of the cylinder, the arrangement being such that towards the end of the movement of the valve member into engagement with either of said valve seats the piston enters a closed end portion of the cylinder over which said slot does not extend, whereas over a major portion of the movement of the valve member between said valve seats the piston is disposed in a region of said cylinder over which said slot extends.

3. A change-over valve as claimed im claim 2 wherein said dash pot cylinder and said piston are disposed within said valve chamber, so that the fluid flowing through the valve chamber forms the working fluid in said dash pot cylinder.

4. A change-over valve as claimed in claim 2 or claim 3 wherein the arrangement is such that the piston approaches the same closed end of said cylinder toward the end of its movement towards either of said valve seats and is furthest from said closed end in said intermediate position of the valve member.

5. A unit comprising two independently operable centrifugal pumps and a change-over valve according to any of claims 2 to 5 having said first and second passages connected with the outlets of respective said centrifugal pump and said third passage connected to an outlet of the unit.

6. A change-over valve substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.

7. Any novel feature or combination of features.

described herein.