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Old 03-20-2016, 09:00 AM   #1
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Jabsco Accumulator Cycle

Hello,
As a relatively new trawler owner ('91 GB 36), I'm not sure what my fresh water pump cycle should be. I had some concern that it was cycling too frequently. There is a Jabsco 30573 accumulator, and I suspected it needed more air pressure.
I have not addressed that, but I did install a new pressure relief valve on the hot water heater, as the old one had developed a leak. And now, the pump sequence is much less frequent when I use hot water. But when using cold water, the pump frequency is the same as before - more rapid. I can move the lever on the galley sink from all hot to all cold, and there is a range, from less frequent to more frequent.
I can check the accumulator air pressure and pump it up if necessary, but I want to understand what the underlying issue may be with the variance in the pump sequence between hot and cold. It makes no sense to me why replacing the hot water tank relief valve would make this happen, and why it would happen at all.
Thank you for any advice!
Mike
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Old 03-20-2016, 09:32 AM   #2
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The first question would be what type of pump is presently being used ? Many newer pumps are variable speed, "on demand" type pumps that do not require an accumulator tank. In fact the tank will confuse the pump somewhat.

If not a variable speed pump, the controlling device for water pump cycling is one (1) pressure sensing switch. There is not one for the hot and one for the cold water. Any drop in pressure to a pre-set pressure point will trigger the pump on and then off as pressure increases. It may be that the volume of water being discharged on the hot water side is less than the volume of water being discharged on the fresh water side. In other words a smaller diameter pipe, outlet, and/or a restriction in a valve.
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Old 03-20-2016, 09:35 AM   #3
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There may be a check valve at the inlet to the water heater. If there is an air space in the top of the water heater, it may act like an accumulator tank giving you less frequent cycling on hot water. The check valve prevents that action from happening for the cold water. Many boat water heaters have side plumbing connections as opposed to top connections. This prevents all the air from venting when you initially fill the tank. To purge this trapped air, turn off the pump and open the hot water valve only, at the sink. Wait till absolutely no more water comes out the faucet. Then turn the water pump on with that faucet open. After water is flowing for 15 seconds out of the faucet, you have likely purged all the air you can out of the water heater.

Ted
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