Water high service pump suction strainer 10 inch pipe

[us_marshal66120]

I am going to replace water suction strainers for a water district inside their clearwell. They are completely submerged, so the use of a foot valve is not essential. They provided me with video that a diver took, but there is no clear view of what is being used now. There is basically a 90 bend flanged to a pipe coming through the wall of the clearwell, into a sump area, with a strainer of some sort bolted to the bottom of it and on the other side of the wall is the pump. There is one pump driven by a 75hp motor, and three driven by 50hp motors.

My question is:

How can I be sure that the basket style strainer I use is suitable for the pumps and wont cause a restriction in flow, cavitation, etc...

Any input would be appreciated.

Thank you

 

[Artisi]

Send the diver back in to video the existing strainer/s. Does the current system work, if not why not - if OK just duplicate it, and if not just rethink the problem.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

Well if you ignore or assume you remove the existing "strainer", which may or may not still exist or may just be a glorified "bolt catcher", you design your system accordingly.

So start with atmospheric pressure at your elevation (converted to metres or feet head of water), add in or subtract height of water (lowest level) above or below the pump centerline respectively, take away any frictional losses at your max flow rate expressed as feet, subtract the NPSHR of your pump at your flowrate and what is left is the maximum differential head across your new strainer.

So to avoid any problem with restriction in flow, cavitation etc, set alarms and monitoring for the pressure across your new strainer so that you clean it when the differential pressure gets too high.

Of course the strainer size is important and also how much material is in the water in the first place. Any large amount of material clogging the filter would be bad and any possibility of things like plastic bags or other film like material is nearly fatal to a basket type strainer.

If this existing strainer is so hard to get at one wonders why it is there? How is it cleaned - back flush?
Why are you replacing it?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mk3223]

Since not clear for the type of the strainer from the video, can you take out or lift the suction pipe to check the strainer first by shutting down one of three pumps?

 

[bimr]

The strainer manufacturer should be able to provide the design information.