How to adjust Jabsco fresh water pump system pressure?

[Skylark]

My Jabsco Para Max 4 fresh water pump is a 30 psi version. It seems that this is a "special" pump for a stack system, not supported with spares (the facts that it's fitted to a 10 year old Beneteau, the largest boat builder in the world, simply beggars belief but that's a discussion for another day). I've hence had to buy a 25 psi replacement pressure valve. Picture shows the broken pressure valve.




I have been told that I need to adjust the system pressure but I'm not clear on how to do this. The supplier said "the accumulator will currently be set to 20 psi and this will have to be changed to between 7-8 psi"

I've now fitted the new pressure valve but as yet not tinkered with anything else. Observations. Pressure seems lower than before (understandable). Flow almost stops to a trickle before the pump kicks-in. The pump energises for only a short time before stopping.

Here's a picture of the stack.



Not in view, there is what looks like a car tyre valve in the middle of the top end of the white accumulator. If this is the part that needs adjusting, I imagine that access for a pressure gauge and/or pump will be challenging.

Any help and advice would be much appreciated. Many thanks.

 

[VicS]

My Jabsco Para Max 4 fresh water pump is a 30 psi version. It seems that this is a "special" pump for a stack system, not supported with spares (the facts that it's fitted to a 10 year old Beneteau, the largest boat builder in the world, simply beggars belief but that's a discussion for another day). I've hence had to buy a 25 psi replacement pressure valve. Picture shows the broken pressure valve.
I have been told that I need to adjust the system pressure but I'm not clear on how to do this. The supplier said "the accumulator will currently be set to 20 psi and this will have to be changed to between 7-8 psi"
I've now fitted the new pressure valve but as yet not tinkered with anything else. Observations. Pressure seems lower than before (understandable). Flow almost stops to a trickle before the pump kicks-in. The pump energises for only a short time before stopping.
Not in view, there is what looks like a car tyre valve in the middle of the top end of the white accumulator. If this is the part that needs adjusting, I imagine that access for a pressure gauge and/or pump will be challenging.

Any help and advice would be much appreciated. Many thanks.

You can remove the accumulator to adjust the pressure ( in fact best done before installation anyway)

Recommended pressure is 2 to 3 psi below the pump cut in pressure

See the 3rd page here https://www.jabscoshop.com/files/Accumulator and Expansion Tank Instructions ZPWL4 doc595.pdf

IIRC Vyv has posted a method of setting the pressure which does not need the use of a gauge and can be done in situ.
I thought on his website , but I cannot find it. Perhaps he will come this way and explain.

 

[vyv_cox]

You can remove the accumulator to adjust the pressure ( in fact best done before installation anyway)

Recommended pressure is 2 to 3 psi below the pump cut in pressure

See the 3rd page here https://www.jabscoshop.com/files/Accumulator and Expansion Tank Instructions ZPWL4 doc595.pdf

IIRC Vyv has posted a method of setting the pressure which does not need the use of a gauge and can be done in situ.
I thought on his website , but I cannot find it. Perhaps he will come this way and explain.

Yes, thanks Vic.

Turn on the pump with all taps closed. Vent the accumulator of air by depressing the valve. Attach your bike pump and open a tap. The water pump will run continuously. Now use the bike pump to add air to the accumulator. The water pump will run with increasingly longer pause intervals until the air pressure exceeds the water pump pressure, when the pause intervals will reduce again. Remove the bike pump and vent air until.the pause length is at its maximum.

 

[Skylark]

Many thanks to you both, @VicS and @vyv_cox

I've now also looked at the spec sheet for a 25 psi version of the Par Max 4 pump and see that the cut-in pressure is 10 psi. 2-3 psi below is 7-8psi, the values given to me by the supplier. Now I can see context. The Gleghorn Waring instructions tell me to adjust the gas pressure with no water pressure. Whereas your method, Vyv, makes the adjustments dynamically. The instructions also say that the accumulator is nitrogen filled so fully venting it will allow it to escape. I hence think I'll start by measuring the pressure and comparing it to the supplier 7-8psi recommendation? Unlikely to visit the boat for a few weeks, unfortunately so it may be a while until I'm able to try to get it fully resolved.

 

[vyv_cox]

Many thanks to you both, @VicS and @vyv_cox

I've now also looked at the spec sheet for a 25 psi version of the Par Max 4 pump and see that the cut-in pressure is 10 psi. 2-3 psi below is 7-8psi, the values given to me by the supplier. Now I can see context. The Gleghorn Waring instructions tell me to adjust the gas pressure with no water pressure. Whereas your method, Vyv, makes the adjustments dynamically. The instructions also say that the accumulator is nitrogen filled so fully venting it will allow it to escape. I hence think I'll start by measuring the pressure and comparing it to the supplier 7-8psi recommendation? Unlikely to visit the boat for a few weeks, unfortunately so it may be a while until I'm able to try to get it fully resolved.

I assume that nitrogen filling is a relatively recent development, a new one for me. Seems like a good idea to retain it if possible.
However, I filled mine with air using the method in post #3 well over 20 years ago and everything seems to have survived perfectly well. I assume the nitrogen is easier on the diaphragm and the steel(?) body.
You could try my method without venting the nitrogen first, only adding a little air if needed.

 

[PCUK]

You're over-thinking this. Just use the schrader valve to lower the pressure a little at a time until the pump operates as you want. It's not rocket salad!

 

[VicS]

Many thanks to you both, @VicS and @vyv_cox

I've now also looked at the spec sheet for a 25 psi version of the Par Max 4 pump and see that the cut-in pressure is 10 psi. 2-3 psi below is 7-8psi, the values given to me by the supplier. Now I can see context. The Gleghorn Waring instructions tell me to adjust the gas pressure with no water pressure. Whereas your method, Vyv, makes the adjustments dynamically. The instructions also say that the accumulator is nitrogen filled so fully venting it will allow it to escape. I hence think I'll start by measuring the pressure and comparing it to the supplier 7-8psi recommendation? Unlikely to visit the boat for a few weeks, unfortunately so it may be a while until I'm able to try to get it fully resolved.

If you have a tyre pressure gauge that you can use all you need to do is depressurise the water side by switching off the pump and opening a tap or two then slowly vent the gas pressure until you get down to 7 or 8 psi.
Vyv's method aims to get to the optimum pressure, rather than a recommended pressure, without the use of a gauge. It would be interesting to know what pressure you end up at compared to the recommended pressure

Lidl to the rescue Ultimate Speed 5-in-1 Tyre Pressure Gauge - | Lidl UK

and in case you need to increase/top-up the pressure Ultimate Speed Mini-Compressor - | Lidl UK

 

[Skylark]

Thanks again, @vyv_cox and @VicS

I do believe that the accumulator is nitrogen filled for the reasons that you’ve stated. I don’t know what pressure mine is currently holding so my first job will be to measure it. Assuming that it’s >8psi, I’ll lower it to this value. Should I need to increase the pressure, I’ll use a bicycle pump, keep it simple.

Unlikely to be able to travel to my boat, Clyde, for a few weeks but this is top of my jobs list for when I do.

Thank you both, again.