Is there a non return valve on a Par Max 4 pump

[tudorsailor]

My fresh water system has a twin pump which is essentially 2 x Par Max 4. The pressure in the system gently drops over an hour or two and then the pump runs to restore pressure. There are no leaks and the accumulator is fine. I have been advised (by Vyv) that a bit of crud can stop the valve closing so that water drains back to the tank and lowers the pressure. I have looked at the service diagram for the Par Max 4 and cannot see a NRV. Is there one in the supply side? Is the "check valve" what I would take to be a non return valve?
Thanks

 

[Trident]

No, these can run back slightly - you'll find if its frequent that its worth either opening up and checking /cleaning the diaphragm as they can get dirty from particulates in the tank and not seal properly allowing more water to run backwards, or if its really bad you may need a new pressure switch on the end as these can start to fail over time but are a replaceable part.

Also if you have a hot water system, you'll find as the water cools in the calorifier that pressure drops ad this will fire of the PARMax for a tiny burst which is quite normal

 

[Momac]

I opened up my Flojet pump the other week . A tiny bit of limescale crud was in there. After that very quick clean up and re-assembly the pump performance was much improved.
I cleaned the inlet filter at the same time and put a new O ring on the filter lid.

 

[VicS]

My fresh water system has a twin pump which is essentially 2 x Par Max 4. The pressure in the system gently drops over an hour or two and then the pump runs to restore pressure. There are no leaks and the accumulator is fine. I have been advised (by Vyv) that a bit of crud can stop the valve closing so that water drains back to the tank and lowers the pressure. I have looked at the service diagram for the Par Max 4 and cannot see a NRV. Is there one in the supply side? Is the "check valve" what I would take to be a non return valve?
Thanks

This Jabsco Tech video should help
Jabsco Diaphragm Pump not Priming | Xylem UK

See also the spares page on the Jabsco Shop website
Jabsco 31620-0292 - Par Max 4' pressure-controlled pump / Pressurised Fresh Water Pumps / Pumps / Marine / Xylem JabscoShop - Jabsco & Rule Pumps and more - from the experts

( if you don't have a strainer on the inlet it might be a good idea to fit one as it should keep debris out of the pump )
.

 

[Boater Sam]

A pump is by nature that it pumps and has to be a non return valve. In fact it is two, one in and one out.
If the in gets crud in it water will go back to the tank and the pump will start to restore pressure.