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Old 25-02-2012, 11:15   #1
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Variable Flow Water Pump

does anybody have any experience with one of the variable flow water pumps that are on the market?

i am talking about a pump that uses a chip and sensor to measure flow rate (as demanded at the outlet) and varies the power of the pump to keep the outlet pressure constant (irregardless of one, two, or more outlets drawing water from the tank).

it is almost time to put my plumbing system back together. my old system (jabsco pump plus an accumulator tank) worked well, but there was a noticeable change in water pressure as the accumulator was drawn down and before the pump kicked in...so am hoping to get a better result with whatever system goes in next.

the technology in these new pumps looks designed to ensure that water pressure stays genuinely constant, but i was wondering if anyone here has any experience with them and can say if it works or not?

the new pump is priced about the same as the old pump plus accumulator so as there are no significant cost differences my decision will simply depend on what works best.
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Old 25-02-2012, 11:35   #2
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Re: variable flow water pump

My accumulator bladder went bad, so I replaced the still-working pump with a Sure-Flo variable flow pump. I was very happy with it--had no problems whatsoever. The nice thing about it was I gained some extra storage space after tossing the accumulator and the old pump was available as an emergency back-up.
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Old 25-02-2012, 11:45   #3
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Re: variable flow water pump

When they first hit the market several years ago we got some returns on them but it looks like the manufacturers have it figured out now. We haven't a return in a year or more. This is the one we sell the most of: Jabsco 12-24 VDC Sensor-Max 14 WPS - 31750-0000

Be sure to take the pressure tank out of the system, it seems to confuse them.
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Old 25-02-2012, 11:47   #4
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Re: variable flow water pump

I installed a variable flow demand pump to even out the "pulsations" that occured with the pump/accumulator system that I had....will never go back to accumulator type system again! Big bonus was that the waterflow from the shower was evened out so that temperature was always consistant.
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Old 25-02-2012, 12:06   #5
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Re: variable flow water pump

Even variable flow is going to be limited by the max output of the pump right? Another option would be to go without an accumulator, but you would hear the pump every time you opened a faucet.... which might remind you to stop using so much water ! :>)
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Old 25-02-2012, 12:46   #6
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Re: variable flow water pump

AHHH if ya wanta save water, install foot or hand pumps !!!LOLOL Just messin with ya !! Bob and Connie
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Old 25-02-2012, 13:03   #7
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Re: variable flow water pump

Ha! So seriously, how does this work...? So if you have a normal pump, when the accumulator is depleted, isnt the pump operating at normal maximum flow? So what you are missing is the added pressure buildup that the accumulator provides. Now if we consider the variable flow pump, does it somehow provide pressure over and above what a normal pump would when it is maxed? Having trouble understanding how a variable gains flow.... unless it's a bigger output pump to start with.... Do you really need less flow.... ever?
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Old 26-02-2012, 09:55   #8
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Re: variable flow water pump

Accumulator tanks are put in water systems to keep regular pumps from turning on and off very quickly when a faucet is open to less than maximum flow of the pump. The accumulator tank doesn't add any pressure to the system above that of the pump. If you have a water system with the pump controled by a pressure switch and you just open the faucet a little, the pump will turn off and on very quickly and damage the switch. The accumulator tank prevents this. The variable speep pumps will turn on each time the faucet is opened and run until it is closed. It only puts out as much water as is needed by varing the speed of the motor. When controlled by a pressure switch a pump has only two speeds, full and off.
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Old 26-02-2012, 10:01   #9
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Re: variable flow water pump

Quote:
Originally Posted by HopCar View Post
Accumulator tanks are put in water systems to keep regular pumps from turning on and off very quickly when a faucet is open to less than maximum flow of the pump. The accumulator tank doesn't add any pressure to the system above that of the pump. If you have a water system with the pump controled by a pressure switch and you just open the faucet a little, the pump will turn off and on very quickly and damage the switch. The accumulator tank prevents this. The variable speep pumps will turn on each time the faucet is opened and run until it is closed. It only puts out as much water as is needed by varing the speed of the motor. When controlled by a pressure switch a pump has only two speeds, full and off.
Yeah....but.... a pump pushing on an open faucet will never get to it's max pressure. A loaded accumulator tank will be at max pressure.... at least for a short time.
These vari speed units sound pretty cool..... if there isnt more to go wrong! I still dont understand in what situation you would want less flow...? isnt that what a faucet is for?
I CAN understand wanting more flow (like showering!). But then that is really determined by the max output of the pump.... not if it's variable speed. What the accumulator does is store energy that a pump produces in a couple minutes of run time, but cant produce in a short period of time if the faucet is open.
Isnt it kind of like saying: "I have a 300hp car but I want go faster... so I'm going to allow the engine to go slower" HUH?
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Old 26-02-2012, 10:23   #10
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Re: variable flow water pump

Cheechako,

The mistake in your thoughts is that the maximum pressure isn't reached when water is flowing from a faucet. It is... which would result to a pump cycling on & off very quickly, like every second. This is normally handled by the pressure tank (which creates a hysteresis) but also by the new sensor variable speed pumps. The pumps switches on, ramps up to get the pressure up and then slows down to put into the pressure lines what the faucet lets out, nothing more, nothing less.

The Jabsco Sensor is the best IMO. The Shurflo was way too high pressure and could not be adjusted back when I changed over in 2005.

ciao!
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Old 26-02-2012, 10:30   #11
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Re: variable flow water pump

The mistake in your thoughts is that the maximum pressure isn't reached when water is flowing from a faucet.
Actually that was my point!
Thanks for the other info though, that makes more sense.. keeps the pump from cycling at less than max output requirements. I assume with a wide open faucet it still just runs continuously? I always hated accumulator tanks... take up a lot of room and plumbing and you need a decent size one to do much good. They do keep the pump from cycling everytime you crack a faucet though.
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Old 26-02-2012, 10:36   #12
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Re: variable flow water pump

Quote:
Originally Posted by Cheechako View Post
Thanks for the other info though, that makes more sense.. keeps the pump from cycling at less than max output requirements. I assume with a wide open faucet it still just runs continuously?
Not the Jabsco I have (which is the bigger of the two types they sell). It gets to it's max rpm's when I open a third faucet.

ciao!
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Old 26-02-2012, 10:37   #13
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Re: variable flow water pump

I guess I'm not explaining this very well. I'll try again.
In a regular water system, with the pump controlled by a pressure switch, the accumulator tank acts as a reservoir of pressurized water. When a faucet is opened the pump will not come on until the pressure in the accumulator tank drops to the "on" pressure of the switch. The pump will then run for at least several seconds until the pressure in the tank comes back up to the "off" pressure of the switch. If the faucet is wide open the pump may run continously until the faucet is closed and the tank pressure comes back up. If the accumulator tank wasn't in the system, and the faucet was opened only a little, the pump would cycle on and off very quickly, maybe as fast as on for a second and off for a second. The idea is to avoid the quick cycling which can damage the pump and switch.
An accumulator tank system allows the pressure to vary usually about twenty psi between the pump turning on and off. A variable speed pump avoids the quick cycling and trys to maintain a constant pressure at any flow rate.
I see Nick did a good job of explaining it, never mind.
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Old 26-02-2012, 12:35   #14
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Re: variable flow water pump

Shurflo 24V Extreme Smart Sensor 5.7 Fresh Wtr. Pump - 5901-1211

thanks to everybody for their very helpful comments.

it looks like this model (24v) pumps out a very decent 60psi, much like a domestic supply.

with some luck the pulsations and the flow rate drop (between the old pump stopping and then starting again) will be a thing of the past.

just need to make sure i have plenty of water in the tank (and a large calorifier).

many thanks again,

david
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Old 26-02-2012, 13:14   #15
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Quote:
Originally Posted by Honey Ryder
Shurflo 24V Extreme Smart Sensor 5.7 Fresh Wtr. Pump - 5901-1211

thanks to everybody for their very helpful comments.

it looks like this model (24v) pumps out a very decent 60psi, much like a domestic supply.

with some luck the pulsations and the flow rate drop (between the old pump stopping and then starting again) will be a thing of the past.

just need to make sure i have plenty of water in the tank (and a large calorifier).

many thanks again,

david
Exactly the 60 psi that I had trouble with. Leaks popped up everywhere... other pumps are 40-45 psi. I also had a build quality problem where the seal between pump and motor blew out because of the pressure.

cheers,
Nick.
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