thread403-107519 Expansion tanks 1

[roker]

Dear friartuck,

since the chilled water system is a close loop system please advise the following:
1.the circulating pump has no static head since the return line enters the suction of the pump, but when the system is started and the height of the chilled water consumer is let say at 40 meters how the water will reach him? (is it because of the pressure in the expansion tank?)
2.is the pressure in the return line from the hihgest consumer dependent on the level the pressure is measured (e.g. the pressure measured during operation of the pump at 30 m is higher than at 10 m).
3. what is the pressure in the close system when the pump is stopped?

thanks and regards,
roker

 

[quark]

It depends upon the nozzle connection in the expansion tank. If you just take a balancing leg from the tank and connect it to the loop then the pump has to just take the losses in the piping plus pressure drop across the user equipment at the given flow rate.

Suppose, you have a heat exchanger connected at 30m above the pump and connceted your expansion tank, then if there is no significant height difference between top most point of the header and the expansion tank level, your pump suction is at 3kg/cm²g approx, the topmost point should idealy be atmospheric. Otherwise, you have to add the static head of water level in the expansion tank in all cases.

The pressure goes on decreasing on the discharge side till the top most point in the header and then starts increasing in the return line. Apply the Bernoulli's equation as suggested by a fellow member in the other thread.