start up strainers

Just a thought on your predicament. In the air force on some of our piston engines, we had a very fine mesh multi disc filter system and before each flight, it was necessary to rotate the multi 4 finger tungstun blade scrapers through at least one full revolution to clear the meshes in the top and bottom of the individual discs. The residue 'Scum' would then gravitate to the bottom of the filter canister and excess buildup was drained at regular intervals through drain plugs in the canister bases. The filter was a canister system but the filter was circular filter discs, that resembled a discus in shape, with mesh in the top and bottom faces and they were stacked 20 or more deep on a hollow perforated discharge bolt. The bolt had a floating tube almost the size of the interior of the canister and larger than the filter discs which held the fingers in place were attached in a free vertical orientation between each filter disc on the outer edge. The oil entered the outer cavity of the canister and them moved through the discus filter meshes and into the bolt. I believe you could find the filter description in the Pratt & Whitney or Wright engine catalogues.

Question 1. Is sane to keep the fine mesh on these strainers?

Answer 1. In many cases we used to remove the fine strainer after startup, in terms the impurities located at the fluid will not affect the pump operation.

Question 2. Are rubber expansions joints designed to to be separated from a pipe spool 120 times per month to get at the cone strainers?

Answer 2. That is true in case of you have a poor design. But with a good design you can overcome all these problems, such as selecting the proper separation system furnished with proper automated cleaning process.

What about Y-strainer (or any other type) furnished with a drain valve to be opened periodically to discharge all impurities at once. We are an oil refinery, and we have a lot of pumps, which its strainers get maintained every 6 months or more because the strainers furnished with a drain valves.

Hello

I would suggest going to a Basket Strainer which is easy to clean and maintain. As far mesh size what type of pump do you have? What size of particulate will it take? Start up screens are for welding slag and mil scale I would do some research and pull them. Rubber flex joints In my experience never stainless flex, but rubber? buna or viton. If you are in Alberta go to alta strainers for a price.

Try a pre-filter before the final filters to help remove some of the contamination. Then have the operator clean them out when he makes a mistake, after a while he won't make the same mistake

Installing a backwash filter would eliminate the added labor to remove and clean the strainer. The cost of the backwash filter would be made up by the lower mantaince hours. Hydac makes an excellent backwash filter I have used on several applications with great success. A process waste drain is required for this filter to direct the cantaminated wasted away from the operation.

Our oil refinery has debated similar centifugal pump suction strainer issues. General consensus is that suction strainers are meant to protect the pump from solids large enough that they would lodge in the impeller. Removing any finer material (if needed for downstream or process reasons) should be done using discharge side strainers (single or duplex if need for continuous operation).

"Witch hat" type (cone) suction strainers should be used only for temporary use. Basket or Y-strainer type as mentioned earlier is preferrable. But if un-avoidable, we have changed cone perforated plate material to a coarse wire mesh type, of largest opening that will still protect the impeller passages. This will minimize un-necessary pluggage with finer material, like pipe scale.

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Question 1: Sometimes stuff downstream like compressor packing will have small passages that the mesh is supposed to keep from getting clogged where it can be a real problem. You mention an evaporator downstream and without knowing your process I would say be sure that you aren't sending a bunch of impurities downstream that can't be handled before you strip that off.

A big but related yarn:

One time, we had a recip H2 compressor that took chlorine off-gas and compressed it. The gas also had O2 and H2O in it so rust was a major problem. About 2 months after upgrading the compressor to pump an extra 25%, we had low suction pressure on the system. Troubleshooting found a large conical strainer well upstream of the suction of the compressor that had been crushed and had, you guessed it, a lot of rust plugging it up. Rather than clean and replace, we foolishly decided to remove the strainer completely. A month later, we replaced the rings and rider bands on this 10-cylinder compressor. 3 months after that, we did it again. The next 3 months, not only did we do a ring and rider band job again, but we had to hone out a 42" cylinder lining that had become scratched. After the 4th time, we analyzed what was left of the piston rings and found high concentrations of rust and silica, imagine that. Further inspection found the wash tower upstream wasn't functioning properly. The mesh pad in the tower had become so clogged with rust, that it was literally a brick and the free area on the pad wasn't sufficient to cause the entrained water/rust to drop out of the gas stream. The moral: don't be like me.

Question 2: Probably not, obviously the people that designed your pump system didn't want to add headcount so that folks could clean out a strainer. The frequency of the operation suggests that you are just waiting for a safety incident or major equipment failure to happen, and that is something to avoid at all costs. If people are not following the basic bolting guidelines, they will quickly devolve to not following other procedures related to the operation or will one day decide that they don't want to clean the pump strainer again that day and let the pump fall on its face. I can visualize the channel-lock pliers in the hands of the operators right now, rounding off the nuts and tightening with a wrench and 5 lb. sledgehammer!

The real issue though is the scaling and particles. You mention preheaters upstream of the pumps, is it possible that the oil in the water is causing a lot of scaling on the exchanger? I would suspect that the scaling on the exchangers and plugging of the pump screen are more than related, they are probably symptoms of the same problem, namely an impurity that is causing you grief either from the oil or something that is in the water to begin with. I would find the source of your struggle before you alter the indicator that you have a problem.

Start up stainers are for startup and only meant to remove small pieces of material that got in the line during construction such as teflon tape fragments, weld slag, thread fragments, etc. These should be in small quantities and therefore the typical cone inline stainer between flanges is suitable for that. You a way beyond that.

IF you are generating "fines" in your process and if they need to be removed at this point you need to install a line strainer which is correctly sized for this. If you can estimate how much solids are accumulating, you can size a basket or bag filter with any strainer vendor. If you need to continue operation while cleaning, consider a duplex strainer which will allow you to filter through one side and clean the other.

I have read all posts..........@7:45 AM 02/22/08

You might want to consider a cyclonic separator. They function in line with minimal loss of primary fluids and are very adjustable. Many installation use a battery/manifold multiples to handle volume without excess velocity/volume per unit. These function well on irrigation pumps of ground water into drip irrigation system for crops. Removes sand in the pumped produced at sub strata water in high volume applications.

MR. GUY

Many very good posts. I also have mixed experience.

The startup strainers are for startup as noted. To catch construction debris.

Cyclones are great in some applications if you are SURE the solids are denser than the fluid. Otherwise they go with the fluid.

Many times the design does not anticipate the need for strainers. In your case there is a lot of solids that are being trapped in the strainer.

My suggestion is three fold:

1. Are the current solids you are catching acceptable to go with the flow? Where do they end up? (will they damage equipment, overly abrasive, affect product quality, can they react to make something you don't want?)

If yes pull the strainer and get on with production.

2. Is there equipment technology issues that need to be addressed?

I the answer to #1 is yes the system can handle the strained solids, are you sure that the solids are not parts of the upstream equipment and the problem is corrosion, wrong material, changed pH, and an indicator of a catastrophe waiting to happen?

3. Is there formulation technology that is making (or not eliminating) the solids upstream? The reactor design, received quality, procedures, may not be what was designed.

Call the "smart guys" that approved the process and be sure they get samples, reports, observations.

All this is easy for the guy that does not have to do it.

.

The purpose of the strainers is to keep miscellaneous crud out of the pumps. Sure they can be removed - if the pumps and everything else downstream can handle the crud without damage or process impact!

Strainers should not be used as filters for the reasons well-described in this post. It sounds as though the process needs a backwashing filter upstream. The problem needs referral to the local Process Engineer to find a solution; the justification for installing additional equipment is in the economics of saving downtime, maintenance time and replacement parts while the strainers are changed and the expansion joints replaced. Take a large hammer, a bucket of crud and a frown, and go talk to the right person.

I agree with the comments that conical strainers are temporary, and should have been removed from service after the system had been flushed & cleared of all construction debris.

Depending on whether you want to have contact with the debris that is plugging up the strainers you can:

1. Use either a simplex or duplex basket strainer. The benefit of the duplex basket strainer is that you can "valve out" one section and service the strainer while keeping flow accross the unit.

2. Use a scraper strainer (similar to that which the person in the military used).

Maybe the biggest question is: Where is all of this debris coming from, and how do you get it to stop?

Good luck!

This frequent cleaning of strainers gives to me the signal that you'll be needing a backwash type of filter as suggested by one of the commentators, e.g. Yamit.

Rgds

Y.Van Hoof