Pulsing due to parallel pumps

[Pete987]

Hi

I have a manifold for an oil heater that enables 2 pumps to be used in parallel, a ball shuttle valve is used to isolate the pumps from each other (see attached drawing). The system operates between 100 - 350psi.
One pump is used as a backup in case the other pump fails. To optimise the response of the backup pump during a main pump failure the backup pump is always running at a low speed.
However, having the backup pump idling whilst the main pump is supplying pressure to the system causes a low frequency pulse in the system pressure which results in a large vibration in the oil heater.

I believe the pulsing originates from a build up of pressure, from the backup pump, when the shuttle valve is blocking the backup pumps flow. This pressure builds enough to bounce the shuttle valve open periodically.
Does anyone agree with this prognosis or have any other ideas on the cause of the pulsing?
Is there any way of stopping this pulsing in the output pressure line?

Thanks for any advice
Pete

 

[HPost]

Your standby pump is generating pressure against the shuttle valve. When the pressure is enough to push ball off its seat, the pressure will reset and process repeats...ad infinitum.

You need an unloading valve that dumps the standby pump flow until the duty pump shuts down.

HPost CEng MIMechE

 

[IceStationZebra]

Couldn't you just replace the shuttle valve with two one-way check valves? This way they could both flow oil at the same time but would close off if a pump is shut down. One issue you may run into is that check valves are rarely 100% leak free in the closed position, so if one pump is off the other pump may try to turn it backwards or leak past the pump back into the tank.

ISZ