Definition & explanation of well pump drawdown volume & typical drawdown cycle times:
Here we explain how to diagnose & correct water pump intermittent cycling "on-off" when no water is (known to be) running in a building. Well pump & water tank off-use cycling or water pump turning on-and-off: diagnosis & repair procedures.
SHORT CYCLE vs INTRMITTENT CYCLE: Comparison of Intermittent Well Pump Cycling with a Short-Cycling Water Pump Problem or with Lost Water Pressure. INTERMITTENT CYCLING REPAIRS: How To Fix Water Pump Intermittent Cycling
This article defines drawdown volume and time for well or water pump systems. Thanks to a suggestion from reader A.L. we include a table of typical water pressure tank or well tank sizes and we show those tank rated volumes, actual drawdown cycle water volume, and typical drawdown cycle "on" times. Shown at page top, a reader's water pressure tank and her well pump's controls.
This article series explains how to diagnose & repair water pump cycling problems like short cycling, intermittent cycling, continuous pump operation, or well pump chattering.
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Our photo shows one way to measure the actual delivery rate of water at a plumbing fixture: measure the time required to fill a 5-gallon bucket. Note that this is the flow-rate in GPM of the plumbing system including pump, pipes, controls etc.
It does not tell us the capacity of the well to deliver water. For that we'd need to see WELL FLOW RATE. [Click to enlarge any image]
The draw-down volume in a water pump system is the volume of water that can be run out of a pump and pressure tank system before the pump turns on, starting with the pressure tank fully charged and the pump having turned-off at the system CUT-OFF pressure, and ending with the water system reaching the CUT-ON pressure and thus turning the pump back on.
A typical draw-down volume is the rated "equivalent gallons" of a water pressure tank is 20 gallons, 32 gallons, 40 gallons, or sometimes larger.
Just how much time is required to draw down the pressure tank's rated volume depends on the plumbing system's flow rate in gallons per minute but the draw down volume will always be less than the tank's specified "volume".
That difference is a feature of pressure tank design including the requirement that about half of the tank's volume might be used by its air space, and it's also a feature of the operating pressure range of the tank.
The time required for a well pump to re-charge the water pressure tank depends in turn on the pressure tank volume in gallons, the well pump's discharge rate in gallons per minute, and of course the well's flow rate, since a limited-flow-rate well may require limiting the well pump's actual discharge rate.
Keep in mind that a well pump's discharge rate in gpm will be reduced depending on the height to which the pump has to lift or push the water out of the well and into the water pressure tank.
Examples: Amtrol's WellXTrol water pressure tanks are sold in tank volumes from 2.0 gallons to 119.0 gallons.
The actual draw-down volumes of these tanks when operating in a 40/60 psi pressure range will vary from 0.6 gallons (for the WX-101 2.0 gallon tank) to 28.1 gallons (for the WX-350, a 119 gallon tank). A 20-gallon WX202 has a draw-down volume of 6.2 gallons (at 20/40 psi) or 5.4 gallons (at 40/60 psi) or 4.7 gallons (at 50/70 psi).
Now if we're running water into a typical residential bath tub at 4 gpm, that means that if a 20-gallon pressure tank and a 40/60 pressure control switch is going to give us (5.4 drawdown / 4 gpm usage rate) 1.35 minutes of running water (from full at last pump shut-off) or 81 seconds before the pump has to turn on again.
Table of Typical Water Pressure Tank Sizes, Volumes & Drawdown Volumes1
|Well-X-Trol Tank Model No.2||Rated Tank Volume
Drawdown Volume (Gallons) 3
Pump Pressure Range (psi)
Drawdown Time 4
(Seconds or Minutes)
|30/50 PSI||40/60 PSI||50/70 PSI||40/60 psi Example|
|WX-202 XL||26||39||8.0||7.0||6.1||1.75 min|
1. Adapted & expanded (with drawdown time) from
2. Amtrol's Well-X-Trol well tanks are sold in at least 16 different sizes. The table above, adapted from Amtrol's tank sizing data, offers and expands on water tank specifications for typical residential and light-commercial sized well tanks.
3. Drawdown volume in gallons = the volume of water that can be drawn out of a fully-pressurized well tank with pump off until the time that the pump turns on.
4. Example drawdown time = time from start of running water out of a fully-pressurized well tank with pump off until the time that the pump turns on. For the purposes of this example we assume that the water flow rate out of the well tank is at 4 gallons per minute - a typical residential bathing tub spigot flow rate.
We also assume that the well pump pressure control switch is set to turn the pump ON when system pressure falls to 40 psi and that it turns the pump OFF when system pressure rises to 60 psi.
Really? Well no. Actual well tank water volume drawdown cycle times and volumes will vary considerably depending on the pump's delivery or discharge rate, well flow rate, the lift height of water from the well, piping sizes and run lengths, elbows, fittings, friction losses and other features.
Typical well pump discharge rates range from 5 to 40 gpm but may be further limited by well flow rate restrictions and restrictors and by pump lift height.
5. Typical design specifications for well systems using a 3/4 hp well pump expect the pump to be "on" for one to two minutes during water tank re-charging provided that no water is being consumed in the building served.
This well pump drawdown time table © 2016 InspectApedia.com
I'm not sure if my pressure tank is short cycling or not. I've read through much of your info. & can not find a definitive answer. Our tank is a bladder tank. It is at least 13-15 years old. I do apologize in advance, I do not know the specs. of the tank.
But I know by comparison to the tanks I've seen at Lowes, that our bladder tank is rather large, and appropriately so. ~ I've attached an image. (We just replaced the 50g water heater & had the plumbing cleaned up - the image is just for visual aid of the bladder tank size because I believe it may be relevant.)
[Click to enlarge any image]
So these are my questions:
I read somewhere that if a bladder tank clicks on/off more than 6x's an hour, that there is an issue, somewhere.
That more than 6x's an hour is considered "short cycling." But is this referral "6x's an hour" for ALL sized tanks? All I really need to know is, is my tank operating within normal parameters, for a tank in it's size range? Or should I be concerned? Is my tank in fact short cycling?
And lastly; WHEN a tank is operating normally, how often should it click on/off in an hour when not in active use?
Does the size of the tank matter when it comes to switching on/off so many times in an hour when it is idol?? I can not find this info, & I believe it would be helpful to me/others so we have a basis for comparison.
At least for me, if I can recognize that the clicks are getting closer together, I can get proactive before my well pump is damaged.
This question was provided by reader Anon. by email and was posted originally at WATER PUMP INTERMITTENT CYCLING.
Our sketch shows the components of a typical drilled well with submersible pump, courtesy of Carson Dunlop Associates, a Toronto home inspection & education firm cited at REFERENCES. [Click to enlarge any image]
Am I right that your home is served by a private well system and that your well pump is a submersible unit that's in the well?
And also am I right that your pressure control switch (at the water tank) is turning on and off the pump directly? That switch is described at WATER PUMP PRESSURE CONTROL REPAIR
That is to say, there is no second heavy-duty relay control mounted nearby that is actually running the pump? (That second control is used on higher horsepower pumps and is described at WATER PUMP RELAY SWITCH ) If your system does use a second pump control relay you might hear two clicks when the pump turns on or off.
If so, then when the pressure drops in your water system, the pressure switch clicks closed and the well pump turns on. Standing anywhere near the pressure tank and control switch you won't hear anything except that click - that's the pressure control switch relay clicking to "close" to turn on the pump or clicking when it "opens" to turn off the pump.
Now to the question at hand. IF no water is being run out of your plumbing system, that is no faucets or fixtures running indoors, no running toilets, no water supply pipe leaks, no outdoor faucets running, no outdoor irrigation system running, THEN the pump should not be turning on and off as if some fairy godfather were mischievously flipping a switch somewhere.
SO if the pump is turning on and off by itself for no apparent reason, EITHER you're wrong and water is running somewhere in the building (or there's a leak) OR there is a leak outside of the building in the well piping.
For example, a bad check valve or failed foot valve in the well or a hole in well piping will permit water to leak backwards out of the pressure tank and back down the well piping when the pump has turned off. As that drainback leak occurs, pressure in the pressure tank falls, and eventually the pump pressure switch (not the fairy godfather) turns the pump on and you hear a CLICK!
This sort of mystery pump cycling on and off is explained further at WATER PUMP INTERMITTENT CYCLING
An easy way to diagnose this condition is to turn off the main water shutoff valve between your pressure tank and the building. Now if the pump turns on again you can figure the leak is in the well piping.
The advice you read that a pump cycling on and off 6 times an hour as the normal maximum is malarkey.
When no water is being used the pump might finish an "on" cycle, bringing pressure in the system up to the cut-off pressure setting, but after that, as long as no water is being used the pump should never run. I cannot imagine what the heck your "6 times an hour" writer was thinking.
The rate of pump cycling on and off depends on the water usage rate, pressure or water storage tank size, type of water pressure tank, building water piping sizes, lengths, number of fixtures running and even the pump's horsepower or ability to deliver water from the well.
It's possible to run so much water so fast that the well pump simply runs continuously.
It's also possible that a slow leak such as a sneaky running toilet that's leaking so slowly you've not noticed it is wasting water and turning on the pump from time to time when no other water is being used.
Continue reading at FOOT VALVES, WELL PIPING or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see PUMP PRIME, REPEATED LOSS of
Or see WELL FLOW TEST PROCEDURE - how much water can we get from the well?
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(Aug 3, 2014) Robert said:
This page helped me identify that my problem with intermittent pump cycling was due to a leaky foot valve. I really appreciate the availability of this kind of expertise.
(Mar 12, 2014) Mark said:
I would describe our problem as intermittent, (roughly hourly) short cycling, (5 seconds), when no water is being run in building. Normal long cycling also occurs during water use. I am suspecting clogged or defective pressure switch and will check that next. (Deep well, submerged pump, bladder tank)
If you see water pressure below the cut in pressure try tapping on the switch. Clogging can indeed mess up switch operation.
(Mar 13, 2014) Mark said:
I drained the bladder pressure tank, then when I aired it up, the air came out the drain, I concluded that the bladder was ruptured and replaced the tank, as well as the pressure switch, for good measure. However it is still doing intermittent short cycling, (5 seconds), when no water is being run in building, and no leaks have been discovered. When the pump recharges from 30 psi to 50 psi, it takes something like a minute. I don't understand the intermittent 5 second cycling.
Mark, try turning off water into the building; if the system keeps intermittent cycling then we surmise there is a leak between the building and the well piping end inside the well itself.
(July 8, 2014) chris said:
recently upgraded my electric panel from 100 to 200 amp.Now that i have power turned back on my sub/pump(drilled well) has been running nonstop intermittent cycles.1st noticed it when showering,lost all pressure. turned the shower off for bout 5 seconds then back on and had full pressure again. My thoughts were that while the power was off (bout 8 hrs)i had lost my prime even though my gauges were still reading 45.I drained my tank charged it to 28lbs for my 30/50 switch just to eliminate 1 of the potential problems, and im holding the same charge of 45(guessing the switch was adjusted prevoiusly for that reading).when the pump cycles off i noticed i wasnt hearing the audible sound of the contacts releasing. took the cap of the p/switch and checked. the pump is turning off without the contacts realesing. the contacts are still mobile and dont look bad . other possibility is when the electric company came . they did back up bout ten feet from tire to well casing not sure if my line got squished??i dont think so because they were on the other side of the well.does the pipeing go from well direct to house??..any thoughts would be helpfull
We would not expect an electrical panel upgrade to impact the operation of a well pump unless at the same time someone messed with the pump wiring & controls.
Losing prime, if you regain it, won't lead to intermittent cycling. Rather losing prime leads to the pump running continuously without delivering water (which can damage the pump).
I'd dig up that squashed well piping and look for a leak there. That could cause pressure drop and pump cycling.
Keep us posted
(July 12, 2014) Ashlee said:
I had always had issues with my well pump. 5yrs ago I replaced the whole line from my home to the well and even replaced the pump. There is a split on the line to my neighbours but that had always been there and the previous home owners never had an issue. My pump went from turn on (with no water running) every few minutes to almost every 30 secs. It turns on even if when the water is off to the rest of the house
Ashlee there may be a leak in the well piping
(Aug 24, 2014) barbara said:
Pump kicks on when no water is running. Changed pressure switch and pressure tank. it is a submersible pump. Put cut offs in line where pipe comes out of well.When you turn t off pressure stays but when you cut it back on it sounds like it sucks back into the well
Sounds like a leak in well piping or bad foot valve or check valve at the pump in the well. When you shut off the water line at the pressure tank, with a single pipe heading back down into the well, water does not quickly exit the pipe (just as an upside down soda bottle doesn't immediately pour out) as air also needs to enter the piping to displace the water leaving.
But when you turn on water between well piping and house there is a supply of pressurized water easily sending water back down into the well.
Then as pressure drops the pump cycles.
Of course I may be mistaken but that's a reasonable guess.
(Sept 15, 2014) John Esquibel said:
My well has run dry we can't drill new one so we have a 550 gallon tank and we got a water pump hooked to it and then it is hooked to one of the faucets in front of the house. I have installed a Check valve so that the water can't go back into the pump but the pump will still run on and off when nothing is running. There is no pressure tank so what can I do to fix this.
John I want to help but I'm baffled by the description of your system.
Basically if a pump runs when you are not running water, you want to read the diagnostic article found above at
More Reading, titled: WATER PUMP WONT STOP RUNNING
(Oct 7, 2014) Steve said:
I'm having intermittent water pump cycling. About every 4 minutes my pump will turn on for about 3 seconds. I checked for leaking pipes and running toilets but all appears normal. I'm guessing the problem lies somewhere between the well pump and pressure tank (tank is 7 years old). Any suggestions or way I can pin point exactly what the problem is?
Steve if you turn off water into the building and the cycling continues you can bet that it's somewhere between pump and well - including possibly a leak at the pump itself, or the pressure tank.
(Oct 8, 2014) Steve said:
Thanks Dan. The pressure tank doesn't sound water logged. Nice and hollow sounding at the top. I checked the pressure switch and it's opening and closing as it should. Any suggestions on what to do next? Call a plumber right? Trying to educate myself as much as possible.
Steve if you shut off water into the house then watch the pressure gauge - and if you see the gauge fall - then you know there's a leak. Perhaps a bad foot valve.
(Oct 9, 2014) Anonymous said:
Pressure gauge is shot Dan. Doesn't move at all. Have plumber coming over to diagnose.
A stuck gauge, if the equipment runs, means the gauge needs replacement. Check for debris clogging at the gauge port too as that can also mean trouble for the separate pressure control switch.
(Oct 10, 2014) Steve said:
The pressure tank was drained and air pressure checked, 18 psi. He hooked an air compressor up to the tank and recharged it. Had the pressure gauge replaced. The problem is temporarily resolved as the gauge shows a slow loss of air pressure when water is not running to the house. The tank is an Amtrol Champion 32 gallon which is 8 years old. I gather there is a pinhole leak in the bladder and the tank will have to be replaced.
(Dec 21, 2014) Tom Butler said:
I replaced pressure switch and found no water coming out of the bladder tank air inlet, but it is still short cycling. It is coming on at about 40lbs and shutting off at about 60
A more subtle bladder tank failure is a small leak between bladder and air chamber. If that has occurred you may have a partly water-logged pressure tank but since air is still in the top of the tank, pressing the pin in the air valve there won't show water.
If you drain all water from the tank and it's still heavy or sloshes it's got water trapped in the air chamber.
in the more-reading links just above see
WATER PUMP SHORT CYCLING - home
(Jan 7, 2015) Louie King said:
I do not think my bladder tank has enough water holding in it Air pressure is fine and no water coming out of air valve. Pressure switch seams to come on quick 30/50 setting I'm thinking maybe check valve problem
Louie check valve problems often result in loss of prime.
(Feb 19, 2015) chrisrobb60 said:
I have a pressurised potable water system for my house. The pump operates for a few seconds every 1-2 minutes. The pressure switch seem to operate correctly. The water is supplied to the pump via an atmospheric storage tank. There is no leakage within the house from any appliances, toilets, etc. There's a check valve between the tank and the pump. With the osolation valves to the house all closed the pump still opeates as per above. Is the problem the check valve?
(Feb 17, 2015) Adele said:
Well water pump runs exactly every two minutes, regardless if water is on or off. Replaced water tank & guage
Sounds like a failed foot valve or check valve or a leak in well piping
Adele, same as my prior comment to Chris
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