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Old 14-10-2017, 03:55   #1
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Pressure: Water pumps and accumulators

I have an accumulator capable of handling a pressure of 4bar roughly 55-60psi or there about. This is fed by a Jabsco 2.9 gph (I've no idea if those are US or Imperial gallons), with a cut in pressure of 15psi and a cut out pressure of 25psi.

I'm guessing that the pump stops once the accumulator had reached 25psi, which is leaving a significant amount of margin in pressure.

If I go ahead and upgrade to a 4gpm pump capable of 50psi, am I then likely to see a significant increase in pressure at the faucet?

Obviously, I wouldn't spend my money just to get the added pressure. My current pump is of unknown age and questionable quality (like most Jabsco items). My plan was buy a new pump and keep the old one as a back up. If buying a new one, I might as well try to benefit by getting something that closer to the working pressure of my accumulator.
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Old 14-10-2017, 04:29   #2
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Re: Pressure: Water pumps and accumulators

Quote:
Originally Posted by mikedefieslife View Post
I have an accumulator capable of handling a pressure of 4bar roughly 55-60psi or there about. This is fed by a Jabsco 2.9 gph (I've no idea if those are US or Imperial gallons), with a cut in pressure of 15psi and a cut out pressure of 25psi.

I'm guessing that the pump stops once the accumulator had reached 25psi, which is leaving a significant amount of margin in pressure.

If I go ahead and upgrade to a 4gpm pump capable of 50psi, am I then likely to see a significant increase in pressure at the faucet?

Obviously, I wouldn't spend my money just to get the added pressure. My current pump is of unknown age and questionable quality (like most Jabsco items). My plan was buy a new pump and keep the old one as a back up. If buying a new one, I might as well try to benefit by getting something that closer to the working pressure of my accumulator.
i don't bother with accumulators just fit the higher output pump and you will get quantity and pressure you require.

the pump regulates the pressure in the system not the accumulater.

an accumulater allows for expansion as water is heated by your boiler,so the system does not get over pressurised by the expansion of the hot water.
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Old 14-10-2017, 04:31   #3
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Re: Pressure: Water pumps and accumulators

Quote:
Originally Posted by mikedefieslife View Post
This is fed by a Jabsco 2.9 gph (I've no idea if those are US or Imperial gallons), with a cut in pressure of 15psi and a cut out pressure of 25psi.

I'm guessing that the pump stops once the accumulator had reached 25psi, which is leaving a significant amount of margin in pressure.

If I go ahead and upgrade to a 4gpm pump capable of 50psi, am I then likely to see a significant increase in pressure at the faucet?
My understanding is since the pump produces about 1.1 gpm more than the old, the pump would cycle quicker by reaching 25 psi quicker. However the pressure will remain the same until you change the cut it and cut out pressures.

If you change to higher pressures just be sure your system is (was) built to handle it. You would hate to have connections start blowing apart in places you can't reach easily.
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Old 14-10-2017, 04:34   #4
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Re: Pressure: Water pumps and accumulators

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the pump regulates the pressure in the system not the accumulater.
Ahhhh, if that is the case then I say go for it as long as your system can handle it!
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Old 14-10-2017, 05:23   #5
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Re: Pressure: Water pumps and accumulators

Be aware that more pressure often results in more water usage.
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Old 14-10-2017, 05:45   #6
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Re: Pressure: Water pumps and accumulators

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Originally Posted by SV Bacchus View Post
My understanding is since the pump produces about 1.1 gpm more than the old, the pump would cycle quicker by reaching 25 psi quicker. However the pressure will remain the same until you change the cut it and cut out pressures.

If you change to higher pressures just be sure your system is (was) built to handle it. You would hate to have connections start blowing apart in places you can't reach easily.
That's exactly it. The new pump would have a over double the cut out pressure of the old one. The old one would be resigned to the spares draw or repurposed for seawater if suitable.

I have a hot water heater. That's presumably why the boat has an accumulator in the first place. Though since the water heater is electric I tend not to run it too often.
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Old 14-10-2017, 05:58   #7
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Re: Pressure: Water pumps and accumulators

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Originally Posted by mikedefieslife View Post
That's exactly it. The new pump would have a over double the cut out pressure of the old one. The old one would be resigned to the spares draw or repurposed for seawater if suitable.



I have a hot water heater. That's presumably why the boat has an accumulator in the first place. Though since the water heater is electric I tend not to run it too often.
Many people fit accumulators to stop the pump cycling for small amounts of water usage. Increasing the system pressure from 25psi to 50psi will result in a larger volume of water being stored in the accumulator. When you open a faucet, all of that water will come out under pressure until the accumulator pressure drops to the pump cut in pressure of 15psi. This is useful as one can fill the kettle in the early morning, or wash their hands without the dreaded "WHAAAAAA" from the pump waking everyone up (as happens without accumulators).
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Old 14-10-2017, 06:31   #8
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Re: Pressure: Water pumps and accumulators

I gather some Jabsco (Xylem) pumps are made for continuous duty (no accumulator required), and some are designed for.... ummm... periodic? spasmodic? non-continuous?... duty, with an accumulator. Something like that...

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Old 14-10-2017, 09:35   #9
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Re: Pressure: Water pumps and accumulators

Since we are on the subject, our accumulator has an air pressure fitting at the top. Any idea what pressure to fill the bladder?
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Old 14-10-2017, 09:57   #10
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Re: Pressure: Water pumps and accumulators

We had an older Jabsco pump / accumulator system and removed them both (accumulator leak) about a year and a half ago. We also have a 6 gal hot water heater. We replaced it with a Shur Flo variable speed pump - 3.5 gpm and no accumulator. Has worked great so far with no issues at all.
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Old 14-10-2017, 10:06   #11
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Re: Pressure: Water pumps and accumulators

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We had an older Jabsco pump / accumulator system and removed them both (accumulator leak) about a year and a half ago. We also have a 6 gal hot water heater. We replaced it with a Shur Flo variable speed pump - 3.5 gpm and no accumulator. Has worked great so far with no issues at all.
We did the same this year. The pump works fine, quieter than the old pump and it doesn't go on in the middle of the night with the pressure dropped.

The Shurflo pumps say they can only prime from 6 ft. Not sure if that is vertical or horizontal fleet.
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Old 14-10-2017, 10:10   #12
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Re: Pressure: Water pumps and accumulators

Talk about good timing - I'm working on my plumbing system this morning, and re-charging my accumulators/pressure tanks.
For pressurized water systems, the accumulator is more than just an expansion tank for the hot water heater to accomodate the expansion of water when it is heated.
The accumulator acts the same way as a large capacitor in a DC electrical system - it dampens out voltage (pressure) variations. Diaphragm pumps (Jabsco) as are most commonly used for boat/RV water systems put out a pulsating flow of water. The accumulator smoothens out the pressure pulsations. Further, the accumulator provides small volumes of pressurized water allowing the pump to cycle less. Fewer on/off cycles = longer pump life. Finally, if you hear the annoying sound of your pressure pump turining on at night when no one is using any water, it's the system re-pressurizing as pressure is lost through backflow within the pressure pump itself. The accumulator will greatly decrease the number of times this happens. Of course, this all depends on the size of the accumulator. The bigger the better in this case.
The bicycle (Schrader) valve on most tanks is to recharge the compressible element in the tank - air.
Most modern tanks have a membrane that separates the pressurized water from the air charge. You can check the pressure with a tire gauge. Older tanks have no membrane and depend on air that was entrapped in the tank when it was first filled up. Since air is fairly soluble in water, eventually this charge air disappears. These tanks have to be recharged occasionally.
Charge the tanks to a pressure somewhere below the hi-pressure cuttoff and the low pressure cut-in. I charge to 5 psi below the hi-pressure cutoff.
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Old 14-10-2017, 10:11   #13
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Re: Pressure: Water pumps and accumulators

Quote:
Originally Posted by ranger42c View Post
I gather some Jabsco (Xylem) pumps are made for continuous duty (no accumulator required), and some are designed for.... ummm... periodic? spasmodic? non-continuous?... duty, with an accumulator. Something like that...

-Chris
As has been explained in a previous post, the only thing an accumulator tank does is to prevent quick cycling on and off of a pressure switch controlled pump.

If you didn't have an accumulator tank and opened a faucet just a little, the pressure in the line would quickly drop and the pressure switch would turn the pump on. Then because there is no accumulator tank, the pressure quickly rises and the switch shuts the pump off. Then the cycle will repeat, very quickly. This is very hard on the switch and pump. The accumulator tank slows this cycle.

Both Jabsco and ShurFlo make pumps designed to avoid quick cycling without an accumulator tank.

The Jabsco actually varies the speed of the pump to match the demand. If you open a faucet, it will run continuous until you close the faucet, no damaging rapid on and off. Don't install this type of pump with an accumulator tank. It confuses the speed controller. It's also a waste of money and space.

ShurFlo takes another approach to eliminate the need for an accumulator tank. When you open a faucet, the pump turns on and runs at full speed. The excess water that can't go out the faucet is diverted back to the intake of the pump. This also allows the pump to run continuously until the faucet is closed.
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Old 14-10-2017, 10:12   #14
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Re: Pressure: Water pumps and accumulators

Quote:
Originally Posted by Dave Lochner View Post
We did the same this year. The pump works fine, quieter than the old pump and it doesn't go on in the middle of the night with the pressure dropped.

The Shurflo pumps say they can only prime from 6 ft. Not sure if that is vertical or horizontal fleet.
that would be vertical,or as it is called in the industry ,prime,lift and head of water.

All water pumps are measured in discharge capacity (GPM), vertical suction lift, and maximum head lift.

GPM Discharge Capacity is the rate of speed that water flows from the source to the discharge point, measured in gallons per minute. It provides the power to move water quickly.

Vertical Suction Lift is the vertical distance from the water source to the pump. This is important for draining a basement or deep pond.

Maximum Head Lift is the total height from the source of the water to the destination or drainage point. This provides the power to move water over a distance.
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Old 14-10-2017, 10:14   #15
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Re: Pressure: Water pumps and accumulators

My understanding is these tanks can full-fill either one of two functions, as an expansion tank as Atoll described, or as an accumulator tank as Cavalier described. It all depends on the installation.
Accumulator tanks are installed down stream of the pump before the manifold that separates the hot and cold circuits. The expansion tank is installed on the cold water input to the hot water heater, down stream of the non-return valve.
I have never installed an expansion tank on my system, and as far as I know have never suffered a problem. I do have a accumulator tank. I kept the tank in the system even during a short term installation of one of those variable speed pumps that do not need an accumulator tank and were the latest thing 15 years ago. The manual for my tank said the valve on the top of the tank should be set slightly above the cut in pressure of the pump, but I've never touched that valve in spite of the many changes in pumps in the last 17 years. Again, AFAIK, I've not experienced any problems from not adjusting that valve.

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