fluid velocity

Sounds like our old friend water hammer has reared his ugly head again!

I liked your answer with a great sense of humour

nsbs@leos.gov.in

Mr Truman Brain is right - It is the witch doctor.

Do you have a reflux valve?

Check for high spots in line - install air valves.

I had a visitor before I could complete the post.

Stan is also right - Your piping seems to be bad with a lot of bends.

If you could reorganize and reduce the number of bends it should help a bit.

Your bends should be fixed in concrete blocks.

The pipe movement should be evident when starting up as well.

The velocity will have more to do with economics. Over the lifetime of the pipes the additional energy consumption may be a lot more than the savings due to a smaller diameter pipe. It is however difficult to say because the circumstances are not known.

Another warning : the pipes should be covered at least just leaving couplings open before pressure is applied. Uncovered pipes would move.

"The situation I have is extreme pipe movement when pump stops and starts. 12" pipe at 3600 usgpm. plenty of elbows."

What you have is a poorly designed piping system to handle water? flow at 575 ft/min.

The problem is the piping system not the flow velocity.

I had a very similar situation years ago with a pump startup on a grooved mechanical coupling pipe system. The fitters were used to welded pipe offering some natural restraint to thrust loads that the grooved system did not have. Piping at the first turn was swaying 3' both directions. Once we put in adequate sway bracing the motion stopped.

How is your piping joined together?

good morning sir

the fluid velocity in a pipeline depends on the economics. lower the velocity higher the size and in turn higher cost of installation. the lower the size higher the velocity in turn higher energy cost. as a thumbrule for water line we keep 5 to 10 ft/sec and air line it is 50 to 100 ft sec and steam line it is 100 to 200 ft/sec. you may refer handbook like crocker and king and rogers etc.

regards

prasant mohapatrea

vindhya nagar ,india

I can't remember where I heard it but as a rule of thumb I try to keep the velocity of water lower than 2m/s. Above this and you start adding cost with bigger pumps and more power consuption. It is quite staggering when you add up the costs. I recommended an increase of one pipe size at work a couple of years ago because I did the calculations and over a 10 year life span the savings were in the 10s of thousands of pounds at current energy prices. This far outweighed the initial cost of installing the bigger size.

A quick-and-dirty calculation indicates a velocity of 3.1m/s, which is on the upper economic limit for liquid flow. Extreme pipe movement might indicate a lack of support, particularly where the pipe changes direction. Action (pump starting or stopping) causes reaction (the pipe moves where it changes direction).

• Consider ways of adding bracing to the piping to restrain the effect of those reaction forces.
• Consider using a variable-speed drive to ramp-up and ramp-down the pump speed.
• Consider ways of duplicating pipe routes so as to reduce the velocity.
• Consider replacing the pipe, or sections of it, with a larger size, properly designed by an experienced piping system design specialist.

Wouldn't some kind of accumulator help? On a recent canal holiday I visited a water powered pumping station near Bradford on Avon and was interested to see that the 15" main up to the canal (maybe 50ft?) had a large accumulator. Maybe this was to smooth the flow from the large reciprocating pump at the bottom, but the principle is surely to cushion pressure fluctuations, the same?

Having pipes sway some when pumps start and stop is not uncommon. When a pump starts, there are forces that might be 50 psi (estimated pump head) x 100 sq-inches (approximate cross section area of 12" pipe) or 5,000 lbs of force being exerted. The flow is about 10 fps, on the high side but not exceedingly so. Consider increasing the pipe supports.

Try to reduce water velocity inside the pipe by not more than 6 ft per second (2 m per second), therefore to maintain the same flow rate, you have to increase the pipe dia. to be 14" instead of 12".

Please try to redesign all the system, and be care when you reduce the number of elbows to maintain a certain min. of piping flexibility.