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PEACETIME · 18-01-2012, 22:19

I am needing to replace my tank and was wondering if any knows what/if any advantage there is in the tank size? It seems there are two available from WM. Thanks

**GordMay** · 19-01-2012, 04:30

The larger the accumulator tank, the more water can flow between pump cycles.

The accumulator tank has an internal bladder that stores air, holding water in the tank and in your water system under pressure. When a faucet is opened, the water from the accumulator tank will be used first. When the accumulator's storage tank is exhausted, the water pump will turn on to maintain pressure in the water system.

**Tellie** · 19-01-2012, 04:31

It depends what your accumulator tank is being used for. If it's for your house water pressure I'd recommend to eliminate it all together in favor of replacing it with an on demand pump.

smj · 19-01-2012, 04:50

It's always been my belief that the accumulator tank was used with an on demand pump. The accumulator tank helps to give a steady water pressure.

**Pblais** · 19-01-2012, 05:05

You should use the small tank on most boats but when you have a larger boat with longer runs and multiple heads you need the larger tank to even out the pressure. My small Jabsco tank will let my pump cycle 50% when a full tap is open wide. If I had the larger tank it would still cycle 50%. The higher the water volume the larger the tank should be. Personally, more volume just does not have an appeal as my water tank is more limited than many larger boats. Making the flow slow and steady is fine enough for a hot shower but encourages water use to be more considered. The tank wouldn't matter if I didn't need a hot shower.

HopCar · 19-01-2012, 08:50

I think Telly is suggesting the newer style variable speed pumps. They work best without a pressure tank. The more common demand pumps have a pressure switch that turns the pump on when line pressure drops and off when it rises. Without a pressure tank in the line you would cause the pump to cycle on and off very quickly if you just opened a faucet a little. The fast on / off cycle will damage the switch. The newer pumps eliminate this problem by varying the speed of the motor to match the demand. Open the faucet a little and the pump runs slow. Open it a lot and the pump runs faster. The variable speed pumps actually seem to be confused by pressure tanks so if you switch to one you should remove the tank.

**James S** · 19-01-2012, 09:57

Quote:

Originally Posted by Tellie

It depends what your accumulator tank is being used for. If it's for your house water pressure I'd recommend to eliminate it all together in favor of replacing it with an on demand pump.

Plus 1 variable speed.
Check the prices...some of those plastic pressure tanks are ridiculously expensive compared to the pump.

**sailorchic34** · 19-01-2012, 10:27

One problem with the smaller accumulator tanks is that thermal expansion from the water heater can tear the bladder rubber over a pretty short period of time. This happens when the water heater goes from cold to hot, say when your on the hook and run the engine to make hot water between anchorages. I had one that lasted less then 4 months this way.

I'm using a larger metal one which gives about 1/2 gallon before the pump turns on. No problem with the water heaters thermal expansion either. You might also check the box stores for a domestic hot water expansion tank. Its the same thing really and perhaps a few dollars less for a bigger capacity...

BTW you can use one on a VSD pump, just add a check valve in line between the pump and tank. This is done on large commercial domestic water systems all the time. Least the ones I've designed anyway...

**bstreep** · 19-01-2012, 18:41

I'll agree with the rest. A VSD pump doesn't need an accumulator. Buy a new VSD, and kill 2 birds with one stone.

**sailorchic34** · 19-01-2012, 20:00

I for one am not really a fan of VSD pumps for low flow applications. Low flow for me is being under 50 GPM btw. From a straight engineering standpoint the pump impeller is less efficient at lower speeds. There is a efficiency loss for the VSD drive too. For the amount of work done, the energy use would be overall higher. Plus there is parasitic power loss of the VSD monitoring pressure 24/7. Oh its small but its there and adds up. Even a 50ma load is over one amp in 24 hours.

Where a pump runs a lot then VSD makes sense. But for the low demand (on / off) applications that boat pressure water systems represent, its a bit overkill and maybe marketing hype. For me a single speed pump with an accumulator offers simplicity, lower cost of ownership and operating costs (IE daily power usage) overall lower then a VSD pump. That's my professional engineering opinion.

Randal Johnson · 19-01-2012, 22:45

If you have a water heater you need an expansion tank. Our boat came with a variable pump but no tank. We found that if we used a significant amount of hot water and left the system unused for a while, the pressure would go over 150 PSI and water would come out the safety valve. I thought it was a faulty valve and replaced it. The new one did the same thing.
About the same time we discovered sometimes the electric head solenoid valve would not open until we opened a faucet. It finally occurred to me what was happening and I added a tank and that cured all the problems.

PEACETIME · 19-01-2012, 22:45

Thanks for your response I am thinking that the 1 gallon powder coated tank at the box store is what I will try. If my pump goes out I might think of a VD pump then but it is not needed now as my old Pur pump is still working. The price of the 1 liter plastic tank from WM vs. the 1 gallon is just crazy.

boden36 · 19-01-2012, 22:55

If you go to a motor wrecker, the plastic pressure tank from a VW beetle windscreen washer works well and is easy to adapt.
Regards,
Richard.

delmarrey · 19-01-2012, 22:56

Quote:

Originally Posted by sailorchic34

One problem with the smaller accumulator tanks is that thermal expansion from the water heater can tear the bladder rubber over a pretty short period of time. This happens when the water heater goes from cold to hot, say when your on the hook and run the engine to make hot water between anchorages. I had one that lasted less then 4 months this way.

I'm using a larger metal one which gives about 1/2 gallon before the pump turns on. No problem with the water heaters thermal expansion either. You might also check the box stores for a domestic hot water expansion tank. Its the same thing really and perhaps a few dollars less for a bigger capacity...

BTW you can use one on a VSD pump, just add a check valve in line between the pump and tank. This is done on large commercial domestic water systems all the time. Least the ones I've designed anyway...

You need to install a check valve between the tank and water heater. The expansion should go out a pressure relief valve in the Municipal inlet line, rather then back up the line. The over load can dump over the side or in the bilge, whichever one choses. Just go 10% to 15% over the pump pressure, with the relief valve.

.