Pump hysterisis

This is posted by ShawnB in reply to lead/lag pump control post(May 2001):
"Remember to keep in mind any mechanical effects: are all of the pumps the same size? Are they the same basic design? Provide for hysterisis to prevent hammer. What size (hp and flow) are these pumps."

Can somebody tell:
-The definition of hysterisis (in photoelectric sensor it is the difference in distance between switching On and Off.)
-What is hammer effect?
-Do we prevent hammer effect in the PLC ladder logic?

Thanks
ahd

I don't know is hammer efect equal than cavitation, but when liquit is flowing, there are energy 1/2 mv^2 where m=mass and v is velocity.
Acceleration and deceleration of flow is not wery simple thing. Maybe Tom Jenkins will tell more about it.

Read this for hammer effect.
www.setra.com/tra/app/app_flu.htm

Hysteresis

This term is commonly applies to electrical theory but can be applied to any field that uses force.

Definition: The lagging of an effect behind its cause, as when the change in magnetism of a body lags behind changes in the magnetic field.

The explanation of water hammer on Godfrey's post is better than anything I could do! If you want an example, jsut turn the faucet in an old house off very quickly - the banging you hear is water hammer.

I'm not sure what Shawn was referring to by hysteris - perhaps he could explain.

You can prevent water hammer by not starting and stopping pumps quickly. You can't do it directly in the PLC, but of course the PLC prgram plus your control elements can be used to limit sudden changes in flow.

The info in the link is not quite right!

godfrey said:

Read this for hammer effect.
www.setra.com/tra/app/app_flu.htm

Click to expand...

The referenced web page gives the correct formula, but does not describe it correctly. I should say

delta Pressure = denisty * sonic velocity * delta Velocity.