Chiller COOLING TOWER STRAINERS Question

[Chilly56]

We have a large cooling tower water Y strainer where I work installed installed after the pump on the condenser water loop for our chiller system. A young engineer there has installed a fine mesh screen around the original strainer to help catch smaller particles. It's causing the Delta T across the strainer to go higher. Was 1 to 2 psi diff now 3 to 4 psi dif and start up. After 24 to 48 hours it's about 10 to 14 psi. It's effecting the discharge pressure and causing the condenser flow control valve to open close to 90 percent. Just wondering if there is a recommendation out there somewhere about how large the filter screen holes should be. Standard strainer was close to 1/8th inch hole and the added screen is 1/32 of an inch. Any suggestions on strainer screen sizes? Thank you!! Chilly.

[WAYNE3298]

If this is a large system you are better off going with a dual basket strainer with the 1/8" holes in the strainer. Either way the 1/32" is too small.

[Spitz]

Do you mean it is installed before the pump?

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[Chilly56]

They're installed on the pump's outlet Spitz. Also thank you Wayne3298 for the advice. I'll mention it at the meeting tomorrow.

[Chilly56]

This whole condenser system is a poor design. Cast iron flapper valves for check valves. No seals. Water always falls back to the tank when the system is shut down. Start up, a wall of rushing water slams into the air eliminators. I had to put soft starts on the pumps to slow down the water when starting the system.

[Spitz]

I would want a low pressure drop strainer before my pump to protect it. There should be a triple duty valve after the pump. If you need a finer mesh filter I would put it on the outlet.

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[WAYNE3298]

Draining back to a tank is normally done to prevent freezing of the Tower basin and outdoor piping. Those check valves should be changed to non-slam. The 1/32" screens are called start-up strainers and are used temporarily for start-up of new systems. Soft start-up is a good idea even if you didn't have a problem.
If they insist on having Y-strainers Sarco makes a scrapper strainer manual and motor driven. The motor driven one can be set up to automatically blow down. They now are running the risk of chiller trips due to the lack of condenser water flow.

[71CHOPS]

I agree that 1/32 is too small. Have a site that had a basket with that size holes, and we’d get service calls every month or so, and have to clean the baskets. Changed to 1/8” and problems greatly reduced.

1/32” to 1/8” is almost a 20% increase in free area.

Anything that makes it through 1/8” is gonna make it through chiller tubes without getting stuck.

[Chilly56]

Thanks Guys! Bringing this info to a meeting tomorrow. I will mention all three of you and your comments. Can't tell you where, but this is a system at a launch pad out at the space center in FL. I appreciate the thoughts.

[WAYNE3298]

You are dealing with the operating contractor. My condolences.

[Spitz]

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[Spitz]

Google search

"bac cooling tower pumping and piping"

There is a PDF that has really good info for you to read up on.

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[71CHOPS]

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That’s funny, how are you supposed to clean them when they are between the pump discharge and the check valve!? Usually the check valve is the triple duty valve.

[WAYNE3298]

I always put a duplex basket strainer on the suction side of the pump. They are big but hold a lot of crap before needing cleaned. With open cooling towers that is important. You can also clean them without shutting the system down. I would never put two strainers in series on the pump discharge.

[jayguy]

I would ask why the filtration needs to be that good. Perhaps there is something in the water? “Normally” you do not need such high filtration after start up.

[Spitz]

This is what I normally see.

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[Chilly56]

Funny too, they say fine mesh. What do they consider fine mesh. 1/8th inch holes??
I removed one of the strainer screens this morning and it is way less than 1/32" More like a 64th. Thank you for all the good advice!

[Chilly56]

Final action of the meeting on the fine mesh screens. Going back to the 1/8" ones that were designed to be in the system to begin with. The opposition was over ruled !!

[pecmsg]

This is what I normally see.

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That's not fair:

No leaking valves
Rusted bolts
4 Tons of crap in the way
Grease and oil on everything
Safety officer busting chops

[Spitz]

That's not fair:

No leaking valves
Rusted bolts
4 Tons of crap in the way
Grease and oil on everything
Safety officer busting chops

And the eyebolt didn't even pull out of the ceiling

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