Pump Protection

[Alanator]

I have gathered a couple of things from this forum, as well as from reading.

Deadheading or low flow - BAD
High flow to the right of BEP - BAD

Ashcroft makes a differential pressure switch with 2 independently adjustable setpoints. I am thinking of using such a device on a transfer pump. I would set one switch to open below a certain differential pressure (high flow) and set the other to open above a certain differential (low flow). I would put a spring-loaded bypass contact around the low pressure switch in order to allow the operator to start the pump.

This almost seems too easy. Am I missing something?

 

[dcasto]

Depends, what if you need to run at a low point for a few days? What if you need to run way out on the curve and you can't afford to shutdown for a small blip in a flow.
DP switches are a pain to operate/calibrate, we have gotten rid of ours and put in pressure transmitters. The PLC subtracts the two pressures and decides high/low shut ins, easy to install and maintain, and they always work.

 

[BigInch]

If a PLC is overkill, as is the case for many applications, a high and a low pressure switch will generally work much better than a dP.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[bingopin]

Depends on the shape of the pump curve and where on the curve the pump operates. A very flat characteristic curve may mean only a few feet of delta head can make a very large difference in flow.

 

[pumpking]

Depends why you want to add this protection, and subject to the process characteristics. Being a mag drive pump manufacturer (

http://www.cdrpumps.co.uk)

we recommend using ALL pumps, not just mag-drive pumps with a digital load monitor, which will protect pumps from operating at either left, or right hand sides of the curve, which can easily be tailored to suit specific applications - if the pump then operates at a bad point, the motor is simply tripped, with the monitor indicating which condition caused the trip to initiate an investigation into what has happened.

If you need any more information, let me know and i can mail something through to you.

 

[stanier]

As you are looking for protection of high and low FLOW conditions use flow switches NOT pressure switches.

A switch could be mounted on the arm of the check valve unless a non slam annulus type is being used. These are really good to prevent damage due to waterhammer.

A non invasive method is an ultrasonic flow switch, strapped on. Several companies make them. If there is a flow meter in the line use that.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au