Pressure Tank – setting the pressure

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How do I set the air pressure in my pressure tank?

The air pressure in the tank should be set according to the low cut-in point of the pressure switch.  Before setting the pressure, it is important to know what the low pressure cut-in is.  There are two ways to determine this.  The first is to find the pressure rating for the switch you installed. This is valid only if the switch has not been adjusted. If the switch was adjusted, the second method should be used, which involves observing the pressure gauge to see at which point the pressure switch turns on the pump.

view of the bottom of a pressure tank

The pressure switch rating is normally written on a tag that is inside the plastic cap covering the switch.  Typically this can be found on the inside of your pressure switch lid.  Before you remove the lid to see the label, you should shut off the power to the switch at the main circuit panel.  To remove the lid, loosen the screw on the top of the pressure switch cap.   Look inside the cover to read the pressure range. The first number is the low pressure  cut-in  pressure.

label inside pressure switch cover

The label on the left is a 30 – 50 pressure switch. Look under the PSI column:  ON/I is the low pressure cut-in pressure, the OFF/O is the high pressure cut-off pressure.

This is the factory setting of the switch when purchased. However, since the switches have adjustment screws, it is possible the switch settings have been changed.

If the switch has been adjusted or you cannot find the rating on the switch, you need to observe the pressure gauge to see when the switch turns on.  You will need power turned on to do this.   Observe  the pressure gauge as you allow water to run in your sink or washing machine.  As the gauge decreases, make a note of where the pressure is when the pump switch activates the pump. This is the low pressure cut-in point. Continue to watch and note the pressure where the pump switch shuts off.  This is the high pressure cut-off point.

Once you have determined the cut-in pressure you can set the tank pressure.  To do so, shut the power to the switch (and pump) off and completely drain the tank of water.  It is important to drain the tank completely before checking and setting the pressure in the tank. If you do not, the pressure will not be set correctly.

There is a valve stem which is usually on the top of the tank under a plastic cap.  With an air pressure gauge, check the air pressure just as you would on a car tire.  It should read 2 to 3 pounds less than the low pressure cut-in pressure.   If the pressure in the tank is not set correctly,  you may then either add or release air as needed.

If you are using a  30-50 pressure switch, the low pressure cut-in point is 30 psi.  Set the tank pressure at 27 or 28 psi.  Once you have the pressure in the tank set correctly, you can turn the pump back on.  Don’t forget to close the boiler valve you opened to drain the tank.

9 Responses to “Pressure Tank – setting the pressure”

  1. ward francis Says:

    very imformitive thank you.

  2. Charles Says:

    Well written and clear. I do wonder if the high switch value has any relevance. I assume not from the text.

    Do not give my eMail address to anyone.

  3. smallgig.com Says:

    This particular post Pressure Tank – setting the pressure Keith
    Specialty Store, features really great information and I
    actually learned exactly what I was looking for.
    Many Thanks.

  4. web site Says:

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  5. Nick Roschinsky Says:

    Hi Keith!
    Maybe you can help me out with my plumbing problem. I replaced my old well x trol bladder tank with a new well x trol wx 202 model because of short cycling. My pressure switch is rated at 30-50. I did not replace the switch, nor have I ever adjusted it. The new bladder tank is pre-charged at 38 lbs. Today my wife informed me that when she flushes the toilet, she hears the water increase in pressure as its filling the toilet tank. I then went into the basement to watch the pressure gauge as she flushed the toilet again. Before she flushed, the pressure gauge was reading 44psi. When she flushed, the pressure gauge gradually dropped to 34psi then very quickly dropped to 28psi which activated the pump, with the pressure rising to 46psi which dropped to 44psi and held. Nearly three gallens of water is required for a flush. The draw for the new bladder tank is 6.2 gal. Our water pump is a deep well pump. Could the pressure switch be bad or could the added pressure in the bladder tank have something to do with it? There are no water or air leaks that I’m aware of. I haven’t checked the air in the tank, should I? Any infomation that you can forward to me would be most welcomed.

    Thank You,

    Nick

    • Keith Specialty Store Says:

      Hello Nick,

      When you installed the pressure tank, if you used a 30-50 switch, you needed to adjust the pressure in the tank down. It comes preset to 38 lbs which assumes you are using a 40-60 switch. When using a 30-50 switch, you need to set the pressure in the tank to 28 lbs. (It is set to 2 lbs below the low pressure cut-in point.) To do this, you must empty the tank, bleed out some pressure until it reads 28 psi, then it should work correctly.

      Try that,
      Good luck,
      Keith Specialty Store

  6. Nick Roschinsky Says:

    Keith,

    Thanks for the info. I checked the air in the bladder tank and sure enough it was pre-set to 38 psi. I turned off the pump and drained the tank, then bled air from the bladder tank down to 28 psi. I then closed the valve to the tank, turned on the power to the pump and activated the pressure switch. I then had the wife draw water untill the low cut-in, then allowed the pump to cycle to the cut-off position, which was 48 psi on the pressure gauge. Slowly, the pressure dropped to 44 psi and remained there untill drawing water again. I ran a cycle a second time and had the same readings on the gauge. The amount of draw was about 4 gallons each time. I’d like to adjust the small nut on the pressure switch to increase the cut-off pressure, to allow the pump a longer cycle time. I’d like the cut-off to be at 50 psi. What do you suggest?

    Thanks again,

    Nick

  7. Nick Roschinsky Says:

    Keith,

    Update! I adjusted the small spring/nut on the pressure switch by turning the nut 3 complete turns clockwise. I then had the wife draw water untill she drew 6 gallons. The drawing of 6 gallons did not complete a cycle. The gauge read 29 psi. I informed my wife to continue to draw water untill the low cut-in activated. When activated, the pump pumped up to 53 psi. I watched the gauge fall to 49 psi, this took a few seconds. I checked the pressure after 40 minutes and it was still holding at 49 psi. It seems that everthing is working fine for now. Again I thank you for your help and advice. Thank god! that there are people like you.

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