What is Pressure Vessel in Booster Pumps

So, what does a booster set pressure vessel do? 

In a very hot humid climate, if the chiller stops to work then the water in the circuit of the HVAC system will starts to expand because of the temperature difference between inside the pipe and the outside ambient.

If the water go on expanding then all the pipe fittings like valves, knobs, ports etc. will have a chance to get damaged and this can lead to a more critical issues.

In order to rectify this issue, here comes the work of pressure vessel, the volume of the pressure vessel is so selected that it is able to accommodate all water currently present inside the piping to avoid the damage to our circuit.

Further the secondary and so on advantages of the pressure vessels are as follows-

A booster set is designed to supply a variable volume of water at a constant pressure.

For example in a large office building there may be anything from a single tap running, needing a tiny quantity of water, to a commercial kitchen running at full speed, needing lots of water. In either case they need reasonable water pressure. The way most modern booster sets achieve this is by having a pressure sensor on the pipework, so as soon as the demand starts (eg. the tap is turned on) and the water pressure in the system drops, the pump/s ramp up until the pressure is maintained. When the demand stops (eg. the tap is turned off again) and the water pressure starts to climb, the pump/s ramp down and stop. The problem with this is that there can be lag after turning the tap on, waiting for the pump to start. There can also be a surge in pressure when the tap is closed, potentially bursting a joint. The pressure vessel provides instant pressure when the tap is opened, and takes up the slack again when the tap is closed.

When a pressure pump is operating, it produces a fixed amount of flow and pressure (an example being 40L/ min at 250kpa). If the tap that you have open only flows 15L/min then the pump is producing more volume than the system can release and the pressure builds.

Once it reaches the off pressure of the switch the pump turns off and the pressure starts to drop. The pressure then will rapidly drop in the pipes to the on pressure and the pump starts again. As the tap is flowing only a fixed amount, then the pump will keep doing this over and over, this is known as cycling. The rapid turning on and off is not good for electric motors, uses a lot of electricity and causes large fluctuations in the pressure which can be annoying. Cycling is even more important when the pump is a submersible bore pump as these are recommended to only start 100 times in a 24 hour period, if it is not controlled, permanent damage can be done to the motor.

If that description is a bit long-winded, think of it this way - imagine taking a dog for a walk with a pole instead of a lead. When you start it jerks the dog forward, and when you stop the dog gets another jolt. Not too comfortable for you or the dog. The pressure vessel is the equivalent of a lead with slack.

Where Do I Install A Pressure Tank?

You install a pressure tank anywhere on the delivery or pressurised side of a system. All pressure pump systems need a check valve (or 1 way valve) installed in the pipework. This can be installed on the suction side (as a foot valve or on the pump inlet) or just after the pump on the outlet. The check valve stops water flowing backwards and the pressure dropping when the pumps turns off. This allows a pressure pump to build up pressure and let the automatic switch turn it off.

A pressure tank can be installed anywhere after this check valve. This means that when all the taps in the system are shut, then the pressure in the system builds. When the water pressure in the system builds to beyond the air pressure sored in the tank, then the air starts to compress and the water fills up the wet side of the tank. Once the wet side of the tank has compressed the air as much as it can, then the pressure builds a little bit more and then switches off.

You simply cut in a T piece or a tapping saddle into the outlet pipework and have a pipe or a piece of pressure hose across to the inlet of the tank. Some tanks (up to about 15L) are OK to mount on the pipe or on top of the pump. Once they get beyond this size, they usually have to be mounted on a base and most of the time they actually come with a base .

Pressure tanks are a cheap, simple and effective piece of gear that will help protect your pump and provide you with a good constant pressure and flow of water for whatever application you need.

References:

1. Southern’s Water Technology
2. Deckpro