Downhill water hammer

[enorl76]

Cary, I was just reading the thread about the golf course irrigation where most of the holes are downhill from the pumping station.  You mentioned that problem that the water wants to keep flowing down when the sprinklers turn off, and what can be done to mitigate that.

I'm seeing something similar I think, I have a 3HP Sta-rite DHJ at the edge of a lake.  The furthest zone is 700ft away and seems to be about 20 ft elevation change.  When the pump turns off (via relay from timer) I hear a clunk clunk from the flapper valve right in the intake flange of the pump. 

I'm assuming this is water hammer from water reversing direction, is there a good way to stop this?

[Cary Austin]

Anytime the pump shuts off while pumping maximum flow rate, as with a relay and timer, the check valve slams shut from the wide open position.  When you valve down the flow rate to like 1 GPM, as is the case when using a CSV, the check valve is barely open and therefore there is no slamming shut causing water hammer.

However, in your case you may simply get rid of the water hammer problem by switching the "flapper" check for a spring loaded check valve.  The spring pulls the check closed as soon as the flow stops and doesn't have to wait for the water to reverse the way a flapper check does.

[Kasey00]

Anytime the pump shuts off while pumping maximum flow rate, as with a relay and timer, the check valve slams shut from the wide open position.  When you valve down the flow rate to like 1 GPM, as is the case when using a CSV, the check valve is barely open and therefore there is no slamming shut causing water hammer.

However, in your case you may simply get rid of the water hammer problem by switching the "flapper" check for a spring loaded check valve.  The spring pulls the check closed as soon as the flow stops and doesn't have to wait for the water to reverse the way a flapper check does.

I have a 3HP Sta-rite DHJ too at the edge of a pond. My check valve is almost closed at 2 GPM. Is it defective then?

[Cary Austin]

Your check valve should be almost closed when the pump is only producing 2 GPM.  It is wide open when you are pumping maximum flow.  That doesn't really have anything to do with the check valve functioning properly or not.  The check valve has failed if it lets water go backwards after the pump has been shut off.