# How to select diaphragm pressure tank

A lot of customers haven’t know how to select a diaphragm pressure tank when they are purchasing the constant pressure water supply device.How to calculate pressure and volume of the diaphragm pressure tank ?Please read the details as below.If you have any problems,please contact us.

Diaphragm pressure tank model selection calculation
Diaphragm pressure tank pressure calculation as below:

1.Safety valve opening pressure P4:the pressure of pipeline and equipment in the system can’t exceed the allowable working pressure.
2.Relief solenoid valves opening pressure P3=0.9P4.
3.Fill pump start pressure P1=the height difference (m) between the fill tank and the peak of system + 3-5M water column.
4.Fill pump stop pressure P2=0.9P3

Diaphragm pressure tank volume calculation
Air diaphragm pressure tank volume calculation as below:

1.Fill pump total hours flow is preferably 5% of the total water capacity of the system,shall not exceed 10%.
2.The adjustable volume of air pressure tank is not less than 3min of fill pump flow.When using variable frequency pump,the fill pump flow can be 1 / 3-1 / 4 fill pump flow at rated speed.

The actual total volume of air pressure tank: V—Pressure tank actual total volume (m3)
Vmin—Pressure tank minimum total volume (m3)
β—Additional volume coefficient,air diaphragm pressure tank for 1.05 P1 is fill pump start pressure(gauge pressure,KPa)

P2 is fill pump stop pressure(gauge pressure,KPa)

Should consider the factors that air pressure tank volume and the maximum working pressure.
The value should be taken 0.65-0.85, if necessary, 0.5-0.9 can be.
Rubber diaphragm bladder volume is not less than diaphragm pressure tank adjustable volume Vt.

Atmospheric pressure diaphragm pressure tank volume calculation as below:
1.Fill pump total hours flow is preferably 5% of the total water capacity of the system,shall not exceed 10%.
2.The adjustable volume of atmospheric pressure tank is not less than 3min of fill pump flow.When using variable frequency pump,the fill pump flow can be 1 / 3-1 / 4 fill pump flow at rated speed.
3.The actual total volume of air pressure tank:V≥Vmin=1.05Vt The configuration of atmospheric pressure diaphragm pressure tank The configuration of air diaphragm pressure tank

The diaphragm pressure tank model selection calculation example
The known conditions as below:
1.The total capacity of the water system is 75000L.
2.Maximum working pressure at the entrance to the circulating pump:1.0MPa
3.Using air diaphragm pressure tank.
4.The height difference between the fill tank and the peak of system is 45M.

Calculation as below:
The air diaphragm pressure tank:
1.Safety valve opening pressureP4=1.0MPa
2.Relief solenoid valves opening pressure P3=0.9 P4=0.9MPa。
3.Fill pump start pressure:P1=45+5=50M water column=0.5MPa
4.Fill pump stop pressure:P2=0.9P3=0.81MPa 5.Fill pump total hours flow75×5%=3.75（m /h）
Get 2 sets which fill pump flow is 2m/h and pump head is 52M.
6.The adjustable volume is not less than 3min of fill pump flow.
Vt≥2×3/60=0.1m3=100L

The actual total volume of air pressure tank:  Select the air pressure tank volume is 400L.