Well pump pressure tank...


My bladder type water tank is rated 20 gallons.
With no water I have 26.5 lbs of air pressure in tank.
The pump cuts in at about 28lbs. and out at about 51lbs.
With the tank full I only get 6.75 gallons of water before the pump runs again. Is this right? If not, what's wrong?
Thanks
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wrote:

If you check pressure tank spec sheets, they will specify the "Draw Down" rating for the different size tanks and pressure switch settings. Draw down is the amount of water you will get between cut-out and cut-in pressures.
A quick check of a brand or two on the web shows 20 gal tanks are rated for about 6 gallons of draw down when using 30-50 settings.
So what you are seeing is about right for that tank with those settings.
Switching to a larger tank will prevent the pump from cycling as often, but you have to balance the capacity of your well and the run time of the pump. A larger tank means the pump runs longer (although less often). This can cause the water level in the well to fall below the pump (low capacity well), and in extreme cases longer run time can cause the pump to overheat.
Many of the tank and pump web sites have guidlines for sizing the tank properly, but you need to know some details about your pump and well. As tanks go, 20 gallons is pretty small.
HTH,
Paul F.
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Get rid of the tank and go with a Grundfos variable speed pump and control system. It pressurizes in a small two-gallon tank while it pumps and only operates on demand. Variable speed means constant pressure. If you set it to 70 psi, turn on the washing machine, flush a toilet at the same time the shower is on, the shower pressure is unaffected. Try that with a pressure tank. I switched last year and I'm very happy.
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wrote:

Yes, but the drawback is sthat the pump runs _every_ time water is drawn. It is the start cycle that is hardest on pumps.
Harry K
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Besides a variable speed pump, the other and more common way to achieve constant pressure is with the use of a cycle stop valve which works in conjunction with a small tank like the OP's 20 gal one. Essentially it's a special valve goes between the pump and the rest of the system and it maintains a constant pressure within a wide range of flow rates. Say it is set to 50PSI. Then it works by throttling back what the pump can deliver so the pressure is 50PSI whether you are getting 2GPM or 12GPM. It will only allow a pressure higher than the set 50PSI at flow rates BEKOW 1GPM. That is done to allow it to then fill the tank up to whatever the cuttoff pressure is, which might be 70PSI.
Which is better is a subject of debate among the manufacturers of the two approaches. One thing is for sure, the cycle stop valve can be used with a regular pump. A variable speed pump is a special pump with more complexity, cost and controls required.
The operation of the OP;s tank sounds about right. The guidelines for those kind of tanks generally call for the tank bladder to be pressurized when empty and drained to 2PSI below whatever the cut-in pressure is for the pump. So with a cut-in of 28, the tank should be around 26. His is 26.5.
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On Sep 18, 5:22am, snipped-for-privacy@optonline.net wrote:

Yes, his system is operating correctly. Oddly, although the standard is 2psi below cut-in, some tanks (and mine included) say 'same as cut- in'. I cannot understand why the pump would ever start with pre- charge at or higher than cut-in. I set mine to 2 psi below.
Harry K
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On Fri, 18 Sep 2009 07:33:31 -0700 (PDT), harry k

The tank pressure only shows up at the pump switch when there is some water in the bladder to transfer it. The pressure drops to zero on the water side when the bladder is empty.
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On Sep 18, 11:52am, snipped-for-privacy@aol.com wrote:

And even if there is some water in it, say a couple gallons, the pressure is going to be lower than the pressure in the bladder. The pressure difference is made up by the tension on the bladder as it stretches. As you pointed out, with an empty tank the gauge will read zero. As you start to pump water into it, the water pressure will gradually rise. It's not going to be instantly equal to the pressure that is pre-loaded into the bladder.
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On Sep 18, 3:29pm, snipped-for-privacy@optonline.net wrote:

1. The bladder 'tension' will not approach cut-off psi. Pressure in both sides will be, for practical purposes, identical. Not sure but I believe the bladder is flacid when the tank is empty (fastened at the bottom, not top). Some of them are replacable without dissembling the tank.
2. The gauge will never reach zero if there is a little bit of water in it.
3. The reason the pressure drops to zero (I overlooked that) is that the bladder blocks the tank exit.
Harry K
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harry k wrote:

It will work with it charged higher than cut in because once the tank is empty the bladder has no more room to move so the pressure coming out of the tank goes to zero even if the bladder has pressure. I'll try changing mine to about .5 psi below cut in. I would think going to the same or higher pressure than cut in would give the system a sort of water hammer type problem when the water stops, or almost stops, then the pump kicks in.
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Yes, but the drawback is sthat the pump runs _every_ time water is drawn. It is the start cycle that is hardest on pumps.
Harry K
_______________________________________
The start cycle is a gradual spinup, not a sudden max speed, so incorrect there. As for pump runs when water is on demand, so what? Ahhhhh, 70 psi.
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Tony wrote:

Thanks everyone, I'll check into some larger tanks. Large is no problem, I've pumped an estimated 5000 gallons out of it in about 6 hours. Note: I extended the 1" main to a 1" frost proof spigot so running the hose full blast keeps the pump running full time instead of turning on and off. Only problem with that was getting brown water with small gravel until it sits for some time. The one time the gravel was enough to block the spigot decreasing the flow, and also making it impossible to turn off! (lucky I put it's own cutoff valve inside)
And as far as pumping so much water and how it will effect my well. My ex FIL worked for a municipal water company for 30 years and now and then they would basically try to run a well dry. The reasoning is because in all the tiny little cracks and crevices in the sides of the well is sediment, and running the well so low helps wash out the sediment and actually improves the wells capacity after some time.
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Ah and t'were possible. My well is 26gpm flow, can't be pumped dry and is still pumping fine sediment after near 20 years.
Harry K
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harry k wrote:

I'm going on what the water company does, I don't know if it is common. I got tired of the sediment in mine and finally installed a filter. I forget how many micron but I'm using the filter that is basically a big spool of string. It's working quite *well*. In a drought my output goes from 20gpm down to as low as 10gpm.
By the way, the water company pumps are 5 or more horsepower, one of them just may be able to run one of our wells dry?
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Yeah, I realized that after posting that there are a lot of pumps out there that will exceed my piddling 1/2 hp :). I also need to be down in the basement flushing out my pressure tank and water heater, both must have a bunch in them.
Harry K
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harry k wrote:

Half a horse and 26 gpm, must have a good well that isn't very deep, or the water table is high, or both. I get 20 gpm tops with a 1 horse pump. It's down about 700 - 800 foot but the real difference is when the the water table goes down and output goes as low as 10gpm (that I have witnessed). Either way it seems my pumping out thousands of gallons of water has very little effect on the water table and/or water output. I suppose I have a lot of reserve in the rock even when the level is low.
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The 26 gpm was teh 'pump down' test after the well was drilled. My 1/2 horse pump doesnt' even come close to that. Well is on a fantatstic aquifer and only 65 ft deep with static level of 10 ft. Neighbor 1/2 mile up the draw from me drilled new well and his came in with static 6" above the well casing. He said he had to let it run open for a week before he could cap it. I don't know wht that did to my well - for sure I have never lacked for water.
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harry k wrote:

You wouldn't believe what I did that night........
I was running the hose and at one point was waiting for a 55 gallon drum to fill. I got a phone call and forgot about the running water. The pump ran for at least 10 hours straight, I'm being conservative. Over 6000 gallons pumped overnight. I don't know what it started at, but after running all that time it was still putting out 10 GPM out of my hose. My electric meter had just been read and a new reading figured my little mistake will cause a jump of about $88 on the next bill. The water got a bit dirty but luckily I recently installed a sediment filter, excluding the outside spigots.
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Say what? 6000 gallons pumped = $88 electric bill? That doesn't sound right. What are your electric rates? Here in NJ we have some of the highest in the country, 18c/kwh and lots of people have irrigation wells installed to avoid paying for municipal water for their sprinker systems. Our water isn't cheap either, $7 per 1000 gallons is the highest rate. Even at that rate, I could buy the 6000 gallons of water for $42.
I'd expect the electric bill for 6000 gallons of water pumping to be more in the $5 range or so for a typical well system.
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On Oct 1, 6:36am, snipped-for-privacy@optonline.net wrote:

Same here.
Harry K
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