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You are here: Home > Sprinkler School™ > Parts and Components > Irrigation Pumps & Pump Start Relays > How A Pressue Tank Works
How Does A Pressure Tank Work?

How Does A Pressure Tank Work?

Pumps - Parts and Components

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Picture of a pressure tank.

Pressure tanks store pressurized water that can be distributed to different areas. The tanks operate by using drops in pressure below a certain point to activate the pumps which replenish the water and raise the pressure. Pressure tanks help to elongate the pumps lifespan because they allow them to run when they are needed verses staying on. They also reduce water hammer instances because they help to keep the water in the irrigation lines at a constant pressure.

Pressure tanks are typically used in conjunction with private wells. The tanks provide consistent pressure to the home's water system within a range of approximately 20 pounds per square inch (psi) and also act as reservoirs, holding extra water in the system. Most home water systems are set up so the pump turns on (cuts in) at 20, 30 or 40 psi and turns off (cuts out) at 40, 50 or 60 psi, respectively. There's a diaphragm in the tank with pressurized air above the diaphragm and a water holding area below.

Pressure Tank, how it works picture 1.
As the water holding area fills, the diaphragm is forced up, increasing the pressure and charging the plumbing system with greater pressure.
Pressure Tank, how it works picture 2.
Once the system pressure reaches the pump cut out pressure the pump stops.
Pressure Tank, how it works picture 3.
Water is drawn from the pressure tank without the pump cutting in until enough water is removed from the water holding area to decrease the system pressure to the pump cut in level.

Example of how a pressure tank and pump work.

After the pump cut in level is reached the pump comes on and runs until the system pressure is equal to the pump cut out level.

The tank allows water to be drawn from the system without the need for the pump to cycle on and off each time the water is turned on. Reducing on and off cycles cuts down on wear and tear and prolongs the pump's life. When choosing a pressure tank you will need to know the gallons per hour (gph) your pump pushes in your plumbing system and the number of plumbing fixtures, including outside spigots, in the system.

Most manufacturers produce a chart that you can plug those numbers into to size your pressure tank. Just remember that if you're in doubt about the size tank you need, it's always better to go with larger pressure tanks. Larger tanks hold more water and reduce the number of times the pump is required to cycle on and off.

- The Do-It-Yourself Sprinkler Store -
 
   
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