What shall I do with a 50bar water discharge?

[andrewfreeman]

Hi Folks,

As part of our test set-up we require very low water flowrates at reasonably high pressures. The spec is water from 5 to 200 litres/hr at pressures up to 50barg. I've looked at 100's of pumps in order to achieve this and have settled for a piston pump with variable speed drive.

However I still cannot get to the lowest flowrates possible therefore I plan to put a bypass on the pump discharge (a branch with a needle valve) to obtain my lowest flows. I know I will be wasting energy but this is for R&D testing purposes only, and the pump will not be constantly running. I have looked into gear pumps, metering pumps, chemical dosing pumps and have not found anything suitable for my flow and pressure requirements.

The pump will be supplied by mains water, pumped from a tank in the basement of our test building using a centrifugal pump.

My question is: Could I feed the bypass line from the pump directly back into the tanks in the basement? This could be water up to 50barg in pressure (fairly low flows though, maybe up to 70 litres/h). Would it cause water to go everywhere, damage the tank, cause excessive noise. If so is there some sort of buffering system I can install to drop the water pressure.

Thanks in advance

Andrew

 

[BigInch]

Doesn't sound like much of a problem. 70 l/h is about 1/3 gallon per minute., even 200 is less than 1 gpm. You are sure about the 70 -200 l/h, then?

Is the tank in the basement a pressure tank or an open tank?

You can handle the 50 barg pressure to an open tank by running the recycle line to the tank and terminating it with an open pipe, so the water "falls" into the top of an open tank, so to speak. As long as there is no fitted connection between the recycle line to a nozzle or a weld onto the tank, the water will be at atmospheric pressure upon exit, although may still have some exit velocity, you will not pressure the tank with an open connection.

To slow the water exit velocity, you could increase the size of the recycle line as it gets closer to the tank. Each increase in size will reduce the velocity and any noise with it, but noise at this low a flowrate shouldn't happen. A partially open globe valves or perhaps a couple of orifice fittings could also be inserted along the way to the tank to decrease the final outlet pressure if needed.

If the basement tank is pressurized, you will need a "hard" connection from the recycle line into the tank. If the tank is pressurized, it should also have a relief valve. Depending on that existing relief valve, you may need to get a valve with the same pressure setting, but capable of handling the extra 50 l/h flow.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[andrewfreeman]

Thanks for the swift reply BigInch. Yes are flowrates are very low. The tank is open topped. I think I'll have to branch into an existing line that returns to the tank. (otherwise make a hole in the floor).

 

[unclesyd]

You might want to look at Milton Roy pumps as we have them working in your required range.

 

[katmar]

200 l/h in a 1" line gives a velocity of about 0.1 m/s. From the bypass on your pump discharge increase the line size ASAP to 1" and lead that back to the supply tank. I don't see a problem. If there ia a bit of noise put some thermal insulation around the reducers.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[BigInch]

If you branch into an existing line that returns to the tank, be sure there are no valves that can be closed between the branch and the tank, otherwise your 50 bars could form behind a closed valve and pressure relief would be required between the branch and the valve.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[MikeHalloran]

To dissipate the kinetic energy of the stream leaving the bypass, try doing what the waterjet guys do below the table; direct the stream into a bucket of balls.



Mike Halloran
Pembroke Pines, FL, USA