Accumulator pressure

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Veteran Member
Dec 31, 2008
Can someone remind me, please?

Should the accumulator be 2psi less than, or more than, the fresh water pump cut in pressure?
I adjust mine at the water pressure at cutout, e.g. when the system is fully pressurized. I have a water pressure gage right there, and adjust the air pressure to the same. I don't think it's that critical anyway. Probably like horseshoes and hand grenades... close is fine.
I pressurized mine with a hand bicycle pump. How much pressure is that? When it needed some more, I pumped some more. Then it was enough.
What is the cutoff pressure of the pump? Why would I need to know?
I'm guessing here, but maybe to keep the diaphragm in the middle? Too much pressure on either side might keep it bulged. Probably not a big deal either way.
I think that you want it a couple of PSI below the pump cut-in pressure.*

If it's above the cut-in pressure, the diaphragm will push out all of the water from the tank once water pressure hits precharge pressure, and the pressure then will go down almost instantly.* You'd probably never notice it and it won't hurt anything, but I think that's the theory.

If it's more than a couple below the cut-in pressure, you simply don't get as much effect from the accumulator as you might - that is, it takes less water pumped in to get to cut-out pressure, and the pump has to cycle more frequently.

More accumulator-ed*information than anyone wants, I'm sure.
Probably too simple of an answer here, but our little accumulator tank has the proper pressure stamped into the top of the case. So that's how much pressure you put in. Given that we have not had to do anything to the pump or the tank or the pressure in eleven years of year-round use, I guess it's a dirt-simple system.
Piers wrote:

Can someone remind me, please?

Should the accumulator be 2psi less than, or more than, the fresh water pump cut in pressure?
It all depends on what kind of tank you have. If it is one of the larger Shurflo bladder tanks, they are charged to about 20 psig. The little Jabsco plastic bladder tanks use 10 psig. The older plastic tanks that have what looks like a screw in plug on top do not use a bladder and are not pressurized. Drain that tank and open the plug to allow air to fill the tank, the air captured inside does the work. When the air is absorbed the tank becomes "air logged" and your pump will short cycle.

If your tank has a tire valve on it, look on the tank for a dataplate*that shows*charge pressure. If*you can't find that, go to the manufacturer's website and look it up.*

Thanks for all the replies.

I think I'm starting to understand the issue. If the pressure in the tank is more than the cut-in pressure of the pump, the pump will never cut in. So the tank needs to be set at a lower pressure than the pump cut-in. Correct? If so, the tank pressure must be set less than that of the pump cut-in switch - I think. I'll try it and see....
Close, but not exactly. The pressure on the air side of an accumulator varies with the water pressure. As your system pumps up, so does the pressure on the air side of the accumulator. Mine is totally different when I'm hooked to shore water (higher pressure) than when my on-board pump is pressurizing the system. I really don't think it's that critical, and it sure won't stop your pump from coming on.
Some cheapo units have NO diaphram.

Beware as the water will slowly absorb the air in them and eventually it will be 100% warer.

Draining gets it back , but if the pump cycles frequently it might be worth a look.

Remember it will be half full of water when winterizing , so MUST be drained.

The other winter hassle is a sink spray diverter , the do freeze /die.

OK, thanks for all the help. I have found it's a Teel and needs to be pre-charged to 28psi, so that's what I set it to. I'll drain all pressure from the system and then check it.

Again, thanks for the help.

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