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ASHRAE Journal Podcast Episode 32

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This podcast is brought to you by Metraflex. With the invention of the re-engineered, low pressure drop LPD Y-Strainer, Metraflex has been the leader in supplying energy-efficient strainers to the industry. Click here to learn more.

Mike Gallagher, P.E., Fellow/Life Member ASHRAE

Strainers and Their Uses in Hydronic Systems

Join Journal Editor Drew Champlin and Mike Gallagher as they discuss how strainers are used in hydronic systems along with the differences between wye, basket and inlet strainers and address common mistakes when applying strainers.

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  • Host Bio

    Drew Champlin

    Drew Champlin is editor of ASHRAE Journal. He has more than 20 years of experience in the journalism industry, ranging from sports writing to engineering publications.

  • Guest Bio

    Mike Gallagher, P.E., Fellow/Life Member ASHRAE, is President of Western Allied Corporation in Santa Fe Springs, CA., and has 43 years of HVAC experience. After joining Carrier in 1980, he spent 14 years in commercial sales with Carrier in Oklahoma, Texas and California, the last four years of which in charge of commercial sales for Southern California. He has spent the last 29 years as a mechanical contractor at Western Allied. Gallagher’s client responsibilities as a contractor have related mostly to service, retrofit and system optimization in existing buildings. During his career, he has spent time working in four major cities across the United States and has been involved with virtually every type of HVAC system used in the United States.

    Gallagher’s ASHRAE involvement at the society level has included membership on two major standing committees (Research and Standards); Chair of TC 9.12, Tall Buildings; and as a member of various committees. At the chapter level, he was past-President of the Northeast Oklahoma chapter, past-member of the Board of Governors of the South Texas chapter; and currently is an active member of the Southern California Chapter. In the SoCal chapter, he has served on the Board of Governors, as Research chair, and twice organized and taught a full day SoCal Spring Seminar in Psychrometrics. Gallagher has written a monthly technical column in the SoCal chapter’s Sol Air newsletter since 2006.

  • Transcription

    Drew Champlin:

    This podcast is brought to you by Metraflex. With the invention of the re-engineered low-pressure drop LPD Y-strainer, Metraflex has been the leader in supplying energy-efficient strainers to the industry. Visit for more. That's M-E-T-R-A-F-L-E-X dot com. 

    Welcome to this ASHRAE Journal podcast episode. I'm your host, Drew Champlin, ASHRAE Journal editor. We'll be speaking with Mike Gallagher on strainers and their uses in hydronic systems. And Mike had an article on this topic in the July 2022 Engineer's Notebook of ASHRAE Journal.

    Mike Gallagher:

    Well, hi. My name is Mike Gallagher, I am President of Western Allied Corporation in the greater Los Angeles area. Been a ASHRAE person for I think 43 years. First 14 years of my career I was a Sales Rep with Carrier, and then the last 30 or so I've been a contractor and most of my time in contracting has been on the retrofit and service side of things. I seldom get involved in new construction.

    Drew Champlin:

    And to also let everyone know, Mike has another article in our January ASHRAE Journal, so be sure to read that, our first issue of the 2024 calendar. Let's talk about strainers. So first off, Mike, to get to the basics, what is a strainer and how is it used in the hydronic system?

    Mike Gallagher:

    Well, we hope that all we have inside the pipes are liquid. If there's other stuff in there, it threatens to gunk things up. The role of the strainer is to catch that stuff. And the decision that has to be made is usually how fine of a mesh. In other words, how little are the holes? If you go little, little, little, you'll catch everything, but you also create a restriction that's going to cost you in energy and other things over time. So some judgment's required.

    Drew Champlin:

    In this column that you wrote, you lead with "Strainers can be one of the greatest missed opportunities in many hydronic systems." What exactly do you mean by that?

    Mike Gallagher:

    Well, that sort of goes back to what I mentioned earlier about the finer the strainer is and the greater level of protection it provides, it's also the greater energy penalty that it imposes. So one of the questions you have to ask yourself is "Do I even need a strainer? And if I do, do I want it to be in there perpetually or do I only want it in there for startup when, at least in theory, most of the crud is going to be flushed out in the first hour? What am I trying to accomplish?" And I see strainers with very fine mesh used in closed loops where, unless a mistake occurs, after startup they have little or no purpose. And even at startup in some of those scenarios, they probably have little or no purpose, and I see them there. That's energy-dumb, and I'm speaking from a service perspective, they don't really fill a need.

    VAV reheat systems for example, in the hot water closed loop, do you really need a strainer at every hot water coil? I mean, I would say no. Get a decent strainer at the pump, maybe you go with a finer mesh at startup with that pump. But then do you really need a strainer at every hot water coil? I would argue no, I don't think it's worth the energy penalty. Flip side of that is that people often do dumb things with strainers. I am not orthodox when it comes to cooling tower pumps. The typical situation you see is a tower. The sump outlet drops down to a pump, but before the pump there's a strainer. That's typical. Well, cavitation and other issues happen as soon as that strainer starts to plug up. And the tower itself has a coarse strainer, a sheet metal strainer with holes in it. That'll keep the grocery bags and the dead birds and whatever else might be in there out of the pump.

    I personally believe that if you were going to use a strainer with an open loop pump of that situation, it should be on the downstream side of the pump. That way you're not going to risk cavitation, you're not going to be adding to the suction head situation to where you're damaging the pump. And I see that a lot out in the real world. Again, I'm not orthodox. This isn't what I usually see, but if it was up to me that strainer would usually be on the downstream side of the pump. So there's some examples of areas where I wouldn't necessarily do it the way that I see it done.

    Drew Champlin:

    Well Mike, let's talk about some different types of strainers. Mike, what are the differences between Y, basket and pump inlet strainers?

    Mike Gallagher:

    So the Y-strainer is the thing you're used to seeing. It's in line, its major role in life is to keep crud out of whatever's immediately downstream of it. Y-strainers typically are on the coarser side. They typically have larger mesh openings. They don't have to, but that's typically what you see. The main reason that you do it that way is that if you went with a really fine mesh Y-strainer, it would plug up quickly if there's really anything to be strained. The Y-strainer basket surface is small, and so if you have a fine enough mesh that you're going to catch stuff and it's an open loop where you actually have stuff to catch, then it's going to plug up quickly and that becomes a maintenance and operational problem. A basket strainer by comparison is physically larger and heavier. You have to account for the fact that anytime something holding water is significantly larger, it's also heavier so you have to mount it accordingly. But a basket strainer has a lot more surface area.

    I mean, I'm just going to lick my thumb, stick it in the air and say it's 5 to 10 times more surface area than a Y-strainer. And so for that reason, it doesn't have to be cleaned as often. And making stuff maintenance-friendly is the best way to end up with a sustainable operation. And we talk a lot about sustainability today with regard to materials and carbon footprint and a lot of other things, but sustainability has been a real realistic important thing for operations as long as there's been equipment to operate, and coming up with a strainer situation that doesn't have to be cleaned as often is about as sustainable as you can get. Now, pump inlet strainers are a little different story. Virtually, all of the pumps that I am involved with are actually shipped with two inlet strainers if they come with an inlet strainer from the pump manufacturer.

    There's the standard strainer that is intended to stay in there forever and ever, and then there's a liner that is much finer and that is considered to be the startup strainer. So when you start the thing up, the liner picks up the little pipe shavings and whatever else might be in there, then the intent is that after it's run for a relatively short period of time and has gotten that stuff out of the loop and it doesn't take long, it doesn't take very many circuits through that strainer for it to pick up whatever's available, then you shut it down, you remove that liner and then you go forward with life just using the permanent strainer.

    I cannot count how many times over the years, it's got to be more than a dozen that I've run into problem situations, and lo and behold, nobody ever removed that liner during the startup process. And so it just continued to get more and more and more plugged up over long periods of time. And eventually, it led to pump cavitation or other performance issues, just not generating the amount of pressure that it should in a lot of cases. Those are the three kinds, and I am a real advocate of basket strainers anytime I'm concerned about ongoing cleaning because they stand a chance of working.

    There's even dual basket strainers, and in a critical application that's what you want because a dual basket strainer has flow going through both baskets, but they come with the ability to isolate. And so you can clean one at a time without having to shut the other side down. And that means that a guy can actually clean that strainer without shutting down the system. And data centers are a good example, but there's many others of critical applications where if it's worth a basket strainer, it's worth a dual basket strainer.

    Drew Champlin:

    Well Mike, what do we need to know about strainer gaskets? We switched from basket strainers to strainer gaskets here. Hopefully the listeners will not be confused.

    Mike Gallagher:

    So this is one of the pet peeves of every building engineer I've ever known. Those inlet strainers on the pumps, in order to clean those, and I'm not talking just blow down, blow down's fine. You have a way to flush water through there and it'll help to clean. But every now and then, you have to actually take the cover off and remove the strainer basket liner and then you have to clean it all up and put it back. And that's especially true with open loops, and it's particularly true with cooling tower pumps.

    So the issue you get here is that tracking down the gasket that goes with that cover on that inlet side strainer is always more difficult than it ought to be. And building engineers as a group are prone to not clean that strainer if they can't identify the gasket because they've all been through a pain experience where they took it apart, the gasket came apart in pieces and they had nothing to put it back and it leaked forever and then they used some seal tight or some gunk to seal it down and then they could never get the lid off afterwards.

    So they've all lived through some version of that. And so without the gasket, they don't do it. And one of the things I advocate to my consultant friends is that the specification for those pumps and with the inlet strainers should also call for a spare gasket for every one of those pumps. And you say, "Well one spare gasket, what good does that do?" Well, it will be nailed to the wall right by that pump, and the part number of that gasket will be memorialized somehow, I'll guarantee you because nobody will want to go through the grief you have to go through to get the right stupid gasket.

    So again, this is just a little ops thing, but if I'm a consulting engineer and I'm marketing my services to facilities people, I have to put myself in their shoes and I have to understand what are their pain points and what is just a total source of irritation to them. And when you suggest something as minor but as fundamentally helpful as that, you will win over your client because they'll realize you understand something about what it is to be in their shoes.

    Drew Champlin:

    Well, what do we need to know about construction?

    Mike Gallagher:

    Strainers as a whole can be threaded, they can be flanged, they can have grooved pipe connections to hold them in place. Generally the little tiny ones are threaded, and as you get bigger, they're usually flanged. I think the key thing is to recognize that strainers, especially the little ones, can break. If people are taking them apart and they've been permitted to corrode, especially if they're not brass, especially if they're steel body, they can break. And that means that if they're threaded, there needs to be a union there because otherwise you can't take it apart without a real production. And then the material, it also matters.

    Brass will last almost forever, so will stainless. Black iron or steel is a little different story. If it's a closed loop and it's just water, there's nothing wrong at all with steel or any of the carbon-based materials. That would be fine ferrous materials. But if you've got some reason to think that you don't want to do that or if you're running copper pipe, it's smaller and then you want brass. There's not a lot else to be said about that. But it's amazing to me if the consultant has done a specification but nobody has hired the consultant do any construction review. It's amazing how you'll walk in at the end and you'll see two-inch copper pipe hard-connected to a steel strainer. I mean, that shouldn't be done.

    Drew Champlin:

    Mike, you have a section in the Engineer's Notebook column about deciding upon the right mesh. What would you say is the logic behind mesh selection?

    Mike Gallagher:

    So what you're really after is deciding what's the critical particle size and brazed plate heat exchangers are really common in the industry now. Twenty years ago, you didn't see them. But water source heat pump condensers, air-cooled chiller evaporators, that's just the start. We see brazed plate everywhere and the size of the openings there is the driver. And there's a thing to understand that sits behind all this, brazed plate or any plate exchanger. It doesn't matter if it's brazed plate or if it's a plate and frame that's bolted together, it doesn't matter. You've got a lot of parallel pathways for the water to go through that heat exchanger. And so if one of them starts to plug up, you don't have any pressure buildup that would help push the particle through because it just takes all those other pathways. And you can't disconnect it and reverse flow from the discharged side to try to blow it back the other way because again, when you're trying to reverse flow, it just goes through the other pathways.

    So these things plug up very easily if particles that are big enough to bridge the hole get through. The rule of thumb is that you want a mesh size that's slightly smaller than half of the particle size. So to make up a size, if you were going to have a 10 micron particle, you'd probably want a 4 micron mesh opening. Now the origin of mesh, if you read up, Google it and see what you find, is interesting. All the original strainers were made out of threads, metal threads or threads of other materials and how old they are, and the number of threads per inch is the mesh size. The bigger the number of threads per inch, obviously the smaller the opening. And the flip side, the fewer threads per inch, the bigger the opening. Now you'll hear most people today talk about openings per inch when they're explaining mesh and we've gravitated to that. And the coarser the mesh is, the more accurate that is because we don't use threads for that anymore.

    You can punch stainless steel to any hole size you want today with our current technology. And so we don't use woven strainers unless they're very small, very fine. Now the typical mesh I see used for brazed plate, most manufacturers recommend something between 20 and 60, and by far, the most common is 40. It makes sense to check to see what the manufacturer recommends for their situation. Most of the air-cooled chiller manufacturers, anymore or just to protect themselves, provide the strainer that they want used. In fact, most of them have built it into the chiller now at this point because of the nightmares they had when they first introduced brazed plate. But that's not true for say water source heat pumps. And bear in mind, water source heat pumps, while they should be on a closed loop and you would want to see them on a closed loop, often get applied on existing older buildings with open loop condenser water. And there, you need to really use judgment on what mesh you're going to use, and I would definitely be using a basket strainer while we're talking about that.

    If I have plenty of pump pressure, I am often tempted to use a 60 mesh in that application, open loop water source heat pump. But if I do that, I have to have a practical cleaning method because 60 mesh will plug up a lot quicker than 40 and 40 will probably protect the heat exchanger most of the time adequately. I have seen a few exceptions. One of them was just immediately downstream air-wise of a concrete plant. And so I've seen exceptions where really fine mesh was really the only way to go. But again, if you don't set them up to be cleaned easily, then you're going to have problems and the building engineer will just pull the basket out because it becomes such a nuisance. And then months later, all the equipment will be plugged up.

    Drew Champlin:

    Well Mike, moving on to blow down. You mentioned in your notebook hard pipe and hose connections. What are the examples or maybe some cases on where the hard pipe needs to be used and also the same for a hose connection?

    Mike Gallagher:

    So that gets back to the question of what makes it the easiest for the facilities personnel, or the service technician if they don't even have a building engineer and they're just hiring a service company come through periodically and do that. Ideally if you're a consultant, you want to be putting your primary strainers above or within a janitor's closet or you've got some sink arrangement, whether it's a floor sink or a conventional sink. And then off the bottom of the strainer, whether it's a basket strainer or Y-strainer, it doesn't matter, there will be generally a threaded connection. Then you'll run that down to a ball valve and then you either put a hose connection on the bottom of that valve or you hard-pipe it down into a janitor's sink if you've got one of some description. And that's really the best way to do it.

    The hard pipe makes it very simple. All the individual has to do is go throw the ball valve open, he flushes down. If the individual wants to see what crud he's got or she's got, they put a five gallon bucket underneath and blow down into the bucket and then look at it. But the permanent piping makes it easier. And if you are in close proximity to any sink, floor drain, whatever, that's the way to go. Now, the rest of the cases, you want to at least leave a hose connection on the upstream side of that valve so that a hose can be run to wherever they do have a connection.

    Without that, what you're telling the individual who's doing the flushing is that they have to take a bucket, get on their ladder, put the bucket maybe up in a ceiling because it's amazing how many of these strainers you see in a ceiling, put the bucket underneath there, manually do this while trying to hold the bucket in place. You see where this is going, right? I mean, how often is that really going to happen until you have a problem? Well, by the time you have a problem you know about, you've probably damaged something. So just making it easy is the key.

    Drew Champlin:

    Well Mike, in an application where you can't easily shut down the system, what do you do about a strainer if you have to take it apart or clean it up?

    Mike Gallagher:

    Boy, I wish there was an easy answer to that. Especially in a critical application, and there are many of those, when you've got a plugged up strainer and there's no easy way to clean it and you have to shut everything down in order to do it, if it's not 24/7 and you have the luxury of waiting say to the weekend, then that's how you handle it. But you may not have that luxury and it may be a 24/7 device. There are a lot here in LA and I would imagine probably everywhere, there are a lot of server room cooling for individual tenants in high-rise office buildings. And unfortunately, some of those are on open loops. And you can do a lot with blow-down, but at some point you may have to take that strainer apart. And if you don't have two strainers in parallel, which you can do, or a dual strainer like that dual basket I was talking about, shutdown is going to be necessary.

    I've been through many, many cases where some business' central order hub thing, it's a small business. It's not some big data center. It's a data closet, but they get orders at all times and that's why they're up 24/7. They are loath to take that online ordering capability offline to give you a few hour window to do what you need to do. And if it's this big of a pain in the neck to take it apart and clean it, you don't know what you might be running into. I mean, I've had several where we brought a spare strainer with us, whole strainer body, because it had been so long since somebody had to turn that threaded plate off of the strainer itself. We didn't know if it was going to come loose or if it was going to break. And you get the big pipe wrench up there with the cheater on it and you're prying on it, who knows what's going to break loose first? Is it the threads or is it the body of the strainer?

    So what you end up doing if you have a problem is you usually coordinate during their next annual shutdown, and most of them will have an annual shutdown, you coordinate re-piping the thing to give them two strainers. And that would be a really good thing for a consultant to note because it costs almost nothing to put two strainers in parallel at the time you're doing it if they're small, but the service cost later if you have a problem, it's just huge.

    Drew Champlin:

    Well, going back to startup strainers, you mentioned in your column that you have lost count on how many times you have encountered issues where a startup liner has not been removed. Why is that, do you think? And what problems does it lead to?

    Mike Gallagher:

    Well the, "Why is that," is a tough one. I think it's human nature more than anything else. People want to go home at the end of their workday, and it seems the magnetic pull on people on Friday afternoons is even greater than the other days, and it's easy to overlook something or forget something. I don't think there's a service technician or a startup technician out there who deliberately wants to shortcut stuff. I think most of them are pressed to do it either because they're the last person at the job site trying to get something started up so that occupancy can take place or you can come up with your own reasons. But for a lot of those, just human being personality, human nature related issues, it gets missed.

    Again, I've lost track. At least a dozen, maybe two dozen times in my career, I have seen these startup strainers that had never been removed and it took a while before anybody realized it. The order of events is to pull that strainer liner out before the water balance is done. So you ask yourself, "Well if they did a competent water balance, wouldn't they have seen that restriction somehow, some way, gotten a clue that it was there?" There's probably more than one way they might've. But you ask yourself, wouldn't they have seen it? Well, not necessarily because especially if this was a relatively clean loop and that fine mesh startup strainer didn't pick up very much, sure it could be several PSI, but would that necessarily have been noticed? I'm going to say no. And I think that goes back to why does it happen and how does it happen.

    The key thing is to note that it's there somehow and get it out. I ran into one fellow who commissioned data centers, and his rule was that when the startup strainer is pulled out, it is left on site. You do not throw it away. But see, he was hired to go through the whole process. So often, there is no real commissioning agent per se, and the guy who designed or girl who designed this project, they design it and they're done. Nobody retains them to go through and do inspections afterwards. So if I were in the commissioning side of the house, what I would be telling people is that these startup strainers don't leave until I tag them because seeing them out on the floor after they've been removed is the only way you know they were ever pulled out.

    Drew Champlin:

    Do you hear any industry misconceptions or maybe any general ignorance as it pertains to using strainers?

    Mike Gallagher:

    I think the most ridiculous thing I ever see is really coarse mesh Y-strainers being used in front of every kind of a device when a coarse mesh Y-strainer does almost nothing. Now, plumbers do this all the time. Because think about it, plumbers are working off of main pressure from the city water main. There's no pump in the loop frequently in the work that a plumber does. And water lines do break. They break underground and you can get crud in them. So in the mind of many of the plumbers I've known over the years, it makes sense to put a coarse mesh strainer just to stop the gravel pieces and whatever else you might get in the event of a line break. And you want it to be coarse because you don't want it to be a really big restriction.

    I understand that logic when there's no pumps. I get that. Essentially, no energy impact even. That's not true in HVAC. At least in my mind, it's not. I wouldn't be putting a coarse mesh strainer in front of every piece of equipment in my installation. Look at it. Figure out where a good strainer that you put in properly that can be cleaned, that has easy blow down, that if it needs a gasket to take the head off and pull it out and clean it, you get it. And if you want us to go a step better than that, you not only have the gasket, but you have a spare basket. And that way the individual doing the work can take off the top, pull out the bad strainer, put in the clean one, put it all right back together again. You won't need that gasket more than—I mean, you can probably take the top off two, three, four, five times before you're going to tear the gasket and have to replace it.

    But when the time comes, now you've got it, you know what it is, and you've got the part number so you can order another one. And having the second strainer basket means that you can clean the first one at your leisure because you were only down for a short period of time. I mean, that's really the better way to do that and do it at one central location, which if you've got a pump, that's pretty easy to do as opposed to having a jillion little strainers out in the loop that just cause problems. And I will tell you historically, half of them, if it's been in for more than 10 or 15 years, you pull the thing open to clean out the strainer and you find out there's no basket in there because somebody pulled it out because they saw that it had no purpose and it wasn't even in there after the first cleaning.

    Drew Champlin:

    Well Mike, to wrap this up, and I know you touched on it early in the podcast, but what are some common mistakes made when it comes to using strainers?

    Mike Gallagher:

    I think the biggest one is just deciding where to put it, "Do I need it?" Putting it in a way that it can be maintained and cleaned and serviced, getting that spare gasket and probably a spare strainer basket. Those are the kinds of things. Now and then, you'll see a strainer that's piped backwards. And normally we all stand back and laugh and point, and I have actually an ASHRAE presentation that I give to local chapters periodically that I call my wall of shame. And there's at least one picture along those lines in that presentation because it's funny. But those are the kinds of things. I think judgment about mesh size is a big deal and, "Where do I need them? Do I really need a strainer at every device in a closed loop system?" I'm going to advocate no. Those are the kinds of things I would say.

    Drew Champlin:

    Well, that's a great way to wrap up this podcast on strainers and their uses in hydronic systems. Mike Gallagher, thank you so much for joining the ASHRAE Journal podcast.

    Mike Gallagher:

    It was fun, Drew.

    Drew Champlin:

    And this is Drew Champlin, and you've been listening to the latest ASHRAE Journal podcast episode. The ASHRAE Journal podcast team is editor, Drew Champlin; managing editor, Kelly Barraza; producer and associate editor, Chadd Jones; associate editor, Tani Palefski; and technical editor, Rebecca Matyasovski. Copyright ASHRAE. The views expressed in this podcast are those of individuals only and not of ASHRAE, its sponsors or advertisers. Please refer to for the full disclaimer.