Knocking when pump is off

[bberman]

So I have a l1 pump plumbed to the return. Right before the bulkheads I have check valves. When I turn the pump the whole return system knocks and bangs for about 45 seconds then stops.

Has anyone ever had this happen? The pics of the plumbing and tank are in the member tank section.

Thanks for the advice!

 

[axio]

bberman;1096770 wrote: So I have a l1 pump plumbed to the return. Right before the bulkheads I have check valves. When I turn the pump the whole return system knocks and bangs for about 45 seconds then stops.

Has anyone ever had this happen? The pics of the plumbing and tank are in the member tank section.

Thanks for the advice!

I would guess it's the check valves causing the knocking. One or some of them might have gone bad. Is there water draining into the sump during the knocking time period? Are you using the check valves because the sump is too small for the tank?

 

[grouper therapy]

How high is the valve above the water level of the sump?

 

[ff337]

Is it a ball style check valve or clapper valve. Ball style is loud in my experience.

 

[bberman]

grouper therapy;1096782 wrote: How high is the valve above the water level of the sump?

I would say a foot 2-2.5 feet

 

[bberman]

There is water coming back in the sump- the valves are brand new. It is not draining all of the water below the return jets but there is def some water coming back into the sump.

I do have plenty of room in the sump. I could take the valves out if needed but the valves are pretty tight to the bulkheads under the thank... So it would be the one time I would be able to make any type of change to them without having to redo the bulkheads.

 

[grouper therapy]

I think the problem may be that they are too high. You are not getting enough pressure from the top side to "keep" the flapper shut. I would move them down to just above the water level of the sump at full pool. I like to oversize the pipe from the pump as it is advantageous for this scenario and for increased flow. Even if the pump is big enough I'd rather optimize the plumbing for flow and control the volume with valves or controllers.
1.5" or 2" is ideal for these dc pumps.

 

[scuba steve]

Placement of the check valves is the most likely cause. As posted above, they should be just above the sump level and closer to the discharge of the pump

 

[bberman]

I checked and it is the check valves - I am going to try and add a third one by the pump- to see if that will solve the problem - if not I prob have to cut the check valves out... It was installed pretty close to the bulkhead so I may have to redo the bulkhead... Thanks for the advice!!

 

[camellia]

Scuba Steve;1096912 wrote: Placement of the check valves is the most likely cause. As posted above, they should be just above the sump level and closer to the discharge of the pump

+1

Had this issue myself...

 

[Adam]

bberman;1097000 wrote: I checked and it is the check valves - I am going to try and add a third one by the pump- to see if that will solve the problem - if not I prob have to cut the check valves out... It was installed pretty close to the bulkhead so I may have to redo the bulkhead... Thanks for the advice!!

Don't add a 3rd one. It's the 2 you have now that is causing the problem to begin with. When the pump gets turned on the pressure is hitting the valves unevenly which is causing them to open and close until there is enough flow to keep them both open. That is where your banging is coming from.

You only need 1 one just above the output of the pump, within a foot or so is good. Remove both of them that are upstream and put one in, or just above, the sump. Try to put it in the easiest accessible spot for maintenance. Having a ball or gate valve installed after the check valve will allow you to close off the line for maintenance.