Water Everywhere; Could Be a Poorly Selected Valve?
The engineer spent 14 years with the Carrier organization, most recently as a commercial manager for the Carrier distributor in Southern California. Then six years ago, he decided to move over to the service side of the business. Now as sales manager for Western Allied, one of the major commercial contractors in the Los Angeles area, he works with water valves on a daily basis. And he’s got some issues about the ways in which contractors size and select them.
Most contractors don’t have a problem with valves that are used strictly for on-off applications, he notes, because it’s difficult to mess those up too badly. Where contractors often get into trouble is with modulating valves — valves that adjust by increments, rather than by either “full-on” or “full-off” operation.
It is these valves that Gallagher most often has to repair or replace, usually because the previous contractor or engineer may not have sized or selected them properly.
Look At Application FirstAccording to Gallagher, the first problem he sees is that many contractors don’t bother to take the application sufficiently into account prior to selecting the valve, especially where modulating valves are concerned.
The first thing to do is determine whether the valve is going to spend all of its life modulating, or if it’s going to be modulating very little.
“If it’s modulating very little, then it’s not a terribly critical thing. But if it’s going to be modulating and hunting and moving back and forth and reacting almost non-stop, then you’d better select a valve that you don’t think is going to start leaking at its seals after a year or two of this. Because that’s where the wear is, and that’s what fails first.”
Through his experience, Gallagher has found that it is often the cheapest valve whose seals fail first — especially in a modulating application where a lot of motion is taking place.
Butterfly valves are a prime example of where contractors may get into trouble. That’s because contractors don’t consider how they operate, and they almost always oversize them in a modulating application.
Gallagher says that butterfly valves are often not a good choice in a modulating application at all, because if the valve is completely closed and then it opens up 15%, about half the water will get through. When the valve is opened up 25% or 30%, probably three-quarters of the water will get through.
“You’ve got a very small modulating range, so if you’re going to use it as a modulating valve, you’re probably going to have to make it smaller than the pipe it’s in,” says Gallagher. And many contractors have a “religious aversion” to sizing a valve smaller than the pipe it’s in. For example, if it’s a 6-in. pipe with a 4-in. valve, it may look a little peculiar, so many contractors wouldn’t even consider that.
But Gallagher stresses that if a butterfly valve is going to modulate at all, it’s usually necessary to use a smaller valve. However, first it’s necessary to examine the application to see if that makes sense.
“I’ve done it many times that way, and it works fine. It may not be the first choice, but it’s an adequate choice as long as you do everything properly.”
Determine Water PressureWater pressure is another important issue that needs to be considered when selecting a valve. A valve needs to be selected that will successfully open, shut, and modulate in the worst-case pressure situation.
A common area where Gallagher sees mistakes made is in hot water heating coils that go with vav boxes, whether it’s for vav reheat or fan-powered boxes with hot water heat.
“The problem there is that those are generally designed with a lot of two-way valves in the system, and then a few three-way valves at the end. As a result, the actual flow through the loop changes quite a bit when there’s a lot of heating called for.
“When it’s cold outside, most of those valves are open, you’re flowing a lot of water, and you’re not building up very much pressure. Many of these valves work fine under those conditions.”
It’s in the spring and fall when it’s a little cool that there could be problems, because a lot of those two-way valves are shut or mostly shut if they’re modulating. What happens is that the pressure builds up in the loop because the pump is pumping less water, and many of the “cheapy valves” (especially the on-off non-modulating-type valves) cannot operate above a certain pressure. Then they either won’t open or they won’t close, and if the pressure in the loop has built up sufficiently so that the valve can’t close, for example, then hot water is circulating through the coil when it shouldn’t be.
During moderate weather, people may not realize this, and the vav box may have to open further and provide more air to overcome that heating coil’s leakage. In the summer, the boiler is shut off anyway, so there’s usually no problem. But there’s still an energy penalty being paid, and most people don’t even know they’re paying it.
Gallagher says a situation like this seldom results in a comfort complaint call from a tenant, which is why it usually goes unnoticed. “Nobody checks to make sure that the valve can successfully operate against the system pressure. And with the cooling and heating sufficiently fighting one another, they’ll keep the space at the right temperature, and nobody will ever know.”
Even if a contractor decides to change out a valve, it’s likely that he’ll replace it with the same size and type of valve. “That’s why energy efficiency consultants can make a living — because there are a half-dozen issues of this sort that are common enough that there are buildings that really do have the issue.”
Too bad the building owner often has to rely on an outside consultant and not his own contractor to provide a solution.
Isolation Valves Are a Pet PeeveGallagher’s biggest pet peeve in the world of water valves comes from isolation valves. He notes that butterfly valves are the cheapest valve around for isolation, but there are two levels of butterfly valve.
“One, the lug style, is flanged, so you bolt it to the piping flange and if you shut off the water, you can disconnect the piping downstream of the valve and remove it, and that’s very nice.”
But then there are the cheaper butterfly valves, the wafer style, where the valve simply sits between the pipe flanges and it all bolts together. That will also shut off and stop water flow, but it’s not possible to disconnect the piping downstream of the butterfly valve.
These valves may cost less and take up a little less space, but according to Gallagher, they are worthless to service contractors and building owners.
“If you’ve got an isolation valve that will stop the water flow, but you cannot then disconnect things downstream, it’s almost worthless. Because you have to drain the whole loop down, get all the water out of the loop to take the piping apart, and that’s the purpose of the isolation valve…or one of them.”
That situation alone causes Gallagher — and probably many other service contractors — to resort to vast amounts of profanity.
Incorrect Valves Affect Touchy ChillersJust how important is a correctly sized valve?
Consider that a correctly sized modulating valve on a cooling tower system will prevent a chiller from getting water that’s too cold at start-up. An improperly sized valve could cause a chiller to receive water that is too cold, and it may just refuse to run.
That’s an annoying problem, because somebody has to go and manually take the chiller through multiple cycles to get it on-line. Gallagher says that correctly sized valves are more critical today, because chillers now have circuit boards on them that just absolutely won’t let you abuse the machine.
“They’ll protect the machine no matter what. And what that often means is that if other pieces of the system aren’t very gentle with the chiller, the chiller will just be very petulant and refuse to operate. And you’ll get these little shutdowns in the spring and fall — season-changing times when you’ve got modulating valves that don’t adequately control condenser water temperatures. It becomes a colossal pain in the neck for the owner.”
Fortunately, it’s not usually difficult for the contractor to isolate the valve as the problem, because he’ll be able to figure out that the condenser water temperature is not being properly controlled. The issue is whether or not there’s an easy — and inexpensive — way to solve it. So size the valve correctly during the initial installation.