Dealing with Low Flow After Installing a Flow Meter – DSP 206

Flow meters are designed to measure how quickly water travels through a filtration system. This is useful for all sorts of recreational water facilities. Pools and spas have been using them for years. Often times health departments will require them for float tanks, as they help provide a certain level of assurance to the filtration quality of a system.

The problem arises when using flow meters that aren’t designed to handle the specific gravity of float tank solution. So far, only one flow meter is designed to be accurate for float tanks and if a system isn’t using that one, it can be a bit surprising to find out that the flow is different. Ashkahn and Graham talk all about the reason for flow meters and how to troubleshoot problems that may cause a loss of flow.

The FlowVis Flow Meter FV-C-Saline (The only float tank tested flow meter)

Listen to Just the Audio

Transcription of this episode… (in case you prefer reading)

Ashkahn: Hi, this is Ashkahn.

Graham: I am a Graham.  And boy do we have a question today. It is, “I installed a FlowViz flow meter on my flow tank, and now I’m getting less flow than I thought I was.”

Ashkahn: Uh-oh.

Graham: Oh. “Did I install it wrong and do I need to run the pump longer now?”

Ashkahn: Okay.

Graham: So let’s-

Ashkahn: Context, let’s start with some context.

Graham: Yeah, let’s give some context. We run a daily podcast.

Ashkahn: My name is Ashkahn. So flow meter-

Graham: Yeah, yeah, flow meter.

Ashkahn: For those of you that don’t know, flow meter is something that you attach to the piping in your filtration system. Usually that tells you how fast the liquid is moving through your system.

Graham: Yep. So, you know this is, if your float tank for instance is 200 gallons and you’re getting 50 gallons a minute through your flow meter as measured. Then you know that it takes four minutes to do kind of a full turnover, which is taking the volume, a full volume liquid of your float tank and pumping it through the system.

Ashkahn: Right.

Graham: So that’s kind of what the flow meter is used for is how long you need to run your pump.

Ashkahn: There’s, yeah, I guess there’s a lot there. Maybe we won’t go into the full depth, but yeah, there’s these things called turnovers. They exist in like pool, that’s like a pool/spa sanitation term for like the amount of time it takes for the full volume of liquid to go through your filtration system. But, because water mixes back in with itself as it comes back out of the filtration system, you don’t actually get 100 percent of the unique water going through the filtration system. So you try to do multiple turnovers to statistically get more water that actually went through once and the way that you kind of can crunch these numbers, in order to crunch these numbers, you have to know how fast the liquid is moving. In order to know how fast the liquid is moving, you have to be able to calculate it somehow and there’s, there are a couple different ways of calculating it-

Graham: Old bucket test.

Ashkahn: Yeah, I mean even like on an ongoing live basis.

Graham: Oh I see. The bucket test by the way is just taking off where your filtration would shoot water back kind of into the tank and instead shooting it into a bucket.

Ashkahn: Into a huge bucket, yeah.

Graham: And if you have, for example, like a 20 gallon bucket, then you take the amount of time it took to fill up that 20 gallon bucket and you can get a sense of what your flow rate is.

Ashkahn: I mean that’s a little, I can’t imagine that really working that well.

Graham: Just do that every hour on the hour.

Ashkahn: I mean at some point your waterline would get too low and you’d damage your pump.

Graham: The reason I know health departments do it on units that have come without flow meters. That’s how they’ve required like bucket tests to even make sure they’re in the realm.

Ashkahn: Yeah, well that’s a bad system. Don’t do that because you want to be able to track the stuff on an ongoing basis because things can change your flow. If you get a bunch of hair caught somewhere in your system.

Graham: That is a float tanks recommend, or the health department’s recommendation, not mine, I’m not advocating this. I’m just the guy over here sharing what advice I can.

Ashkahn: There are ways with pressure valves before and after a pump to calculate flow and stuff like that, but most people do it by having a flow meter. Some sort of device that goes into the piping like we talked about. And the issue is that most of those flow meters that people are looking at are made for pools and spas that are pumping water.

Graham: Wah, wah, wah.  

Ashkahn: We have much higher density liquid than they do and so whether a flow, a given flow meter may or may not be accurate, in my mind is something that should be questioned when you look at a flow meter. At least specifically what we know is that this company named H2flow makes a flow meter called a FlowViz and found that their normal pool one was in fact not accurate on float tanks and so they made a special float tank calibrated one.

Graham: That leads us to believe that it’s likely that other flow meters would not be accurate in the water as well. They haven’t been tested so we don’t know that for sure. But what we do have as a result of that testing is we do know there’s at least one flow meter that does work accurately with float tanks.

Ashkahn: Yeah.

Graham: If installed correctly.

Ashkahn: So your question if you installed it correctly, one, did you buy the actual float tank one or did you buy the pool FlowViz meter? You should check on that because-

Graham: Wah, wah, wah.

Ashkahn: There are different ones. And-

Graham: That intro show really got me into sound effects, we should make a bunch. Kids cheering, soundboard yeah.

Ashkahn: There is a, there’s-

Graham: Wah, wah, wah.

Ashkahn: Your sound effects really threw me off. There are ways to not properly installed the flow meter, although the FlowViz specifically makes it relatively hard to screw it up, most other flow meters are more difficult to install correctly than this one is. A lot of times you need a certain distance of straight piping on either side and you either need it to be like a certain orientation-

Graham: Yeah, vertical or horizontal-

Ashkahn: Vertical or horizontal. Things like that. And for the FlowViz as far as I know you should check in with them, but as far as I know, you can install it horizontally or vertically. And you can, you don’t necessarily need to have straight pipe coming for a certain distance. You can like have pipe the turns and stuff, unless you are doing it with one and a half inch pipe. So they make, I think their standard that they make for their float tank one starts at two inches of pipe. Some float tanks have two inches of pipe, many come with inch and a half. So if you have inch and a half pipe then you need to kind of step up the size to two inches and-

Graham: And that’s referring to the diameter-

Ashkahn: The diameter.

Graham: Just for the pipe layman out there.

Ashkahn: So you should call FlowViz if that’s the case. I think if I remember correctly they want a certain distance of two inch pipe on either end of the flow meter before it steps down to inch and a half to make sure that you’re getting an accurate reading.

Graham: So there are ways it could be installed incorrectly.

Ashkahn: As long as we’re throwing out asterisks and all this, so the other thing you should know is that the FlowViz, while it is calibrated to float tank water, I think it’s calibrated to 1.25 specific gravity, either that or 1.26. One of those two because that’s the rating that the NSF set as their specific gravity when they did their float tank certification testing. And so he went to get this flow meter NSF certified and just decided to go with their exact same specific gravity.

From the studies when he did his bucket test and tested the flow rate through a flow meter, what he found was that the readings were lower, the higher in density you were getting. So if you’re up at like 1.28, 1.29, you might be getting slightly less flow than is actually written on the flow meter there.

Graham: And that at least makes intuitive sense, right? It’s kind of like the heavier the liquid is you’re pumping through the more work the pump needs to do.

Ashkahn: Yeah, so you’re not trying to pump rocks or something like I feel like that would go pretty slow.

Graham: Molten lead. Yeah.

Ashkahn: So okay, now we know what this question’s about.

Graham: Awesome.

Ashkahn: So yeah, if you had a float tank that had some other flow meter maybe it’s from a while ago or something like that and you replaced it with the FlowViz one. Yeah, I wouldn’t be surprised to see that that number is lower than it was before.

Graham: Or even if you just have an older float tank or something and manufacturers have been doing tests on it with a different flow meter to figure out what flow it is. Like they, you know, if this FlowViz hadn’t come out by then they might have a kind of rated it for inaccurate flow as well. So, there are reasons why it would naturally go down, even if you’ve installed it totally correctly and you’d almost expect it to.

Ashkahn: So I guess, what do you do now? One thing I’d do is, is make sure your entire filtration systems like clean and functioning normally, right? Like go and make sure the filter, you put in a clean filter, clean the strainer going into the float tank out into the filtration system. If you have a strainer basket that’s a part of your pump, clean that. Clean your impeller that’s in your pump. Make sure any spot that could have something, hair, something slowing down the system is cleaned out so that you know you’re getting like as best the number that you can.

And at that point, if that’s still lower than what you need to do in terms of turnovers, yeah then things get trickier. You pretty much, if you want to do the same amount of turnovers, is you have really two choices. You either have to-

Graham: Shrink your float tank.

Ashkahn: Shrink your float tank. Yeah, I guess you could shrink your float tank. So there’s three choices, shrink your float tank, run your filtration system longer or upgrade your filtration system. Upgrading is kind of expensive because you can’t just get a bigger pump unless the rest of your equipment is also rated to handle a higher flow rate.

Graham: Although, if everything was sized for a certain flow rate and now it just turns out your pump is getting less. It might be the only thing you do have to replace is the pump and everything is rated properly for what you’ll now realistically be pushing through it.

Ashkahn: So that’s a possibility. You might have an easy out there and if not then you’d have to kind of replace a bunch of stuff.

Graham: And this happened to us, like in our shop we replaced a different, or did we replace them or did we just install flow meters? Anyway, we installed the FlowViz flow meters. The flow was less as a result than we had thought we were getting and we had to lengthen the pump cycles on pretty much all of our tanks.

Ashkahn: Yeah. Yeah. We installed the FlowViz ones before they did any of their testing.

Graham: Yeah, right, right. That’s what it was. I was like, I only remember FlowViz flow meters, but I don’t remember them being-

Ashkahn: And we had to go replace them all.

Graham: So yeah, it kind of sucks, you know, it means that we have to kind of come up with elaborate ways that we can turn on the pumps and make sure that people are out of the tanks, but potentially when they’re still in the room we just don’t have, you know, for some of the pumps we need to run them for 20 minutes in order to get the amount of turnovers that we want. So it wasn’t a fun thing to realize. And you also realize at that moment that you have not been filtering your water as thoroughly as you thought you were beforehand. Right?

Ashkahn: So this is good stuff to know. I mean, I usually recommend everyone has flow meters on, on all of their float tanks because manufacturers can test stuff and they can work perfectly fine in their facility and then something can happen. You get a bunch of hair caught up in somewhere and it’s really hard to know that sort of stuff without being able to see a number that shows the impact on your flow. And so if you’re just kind of flying without that information then you could be going months between when you do your routine cleaning and having lower flow than you want to or then you should.

Graham: Right. And if your flow is like halved, you probably will notice that visually or just kind of see that it seems to be going slower, but if it’s dropping by like 5 or 10 gallons per minute-

Ashkahn: Which is much more often what’s going on.

Graham: Yeah. Then you probably won’t notice subjectively. So without a flow meter, you’re just not going to catch that stuff.

Ashkahn: Okay. Asterisks, it should be mentioned that what we’re talking about right now are float tanks they use a recirculation model with filtration. Meaning that the filtration equipment is piping connected to the flow tank and the solution flows through the filtration system, spits right back out into the float tank. There are float tanks out there that use a reservoir, like an external vat where a filtration cycle is the float tank emptying out of the float tank, filling into an external vat and then emptying back from the vat.

Graham: Basically one giant bucket test.

Ashkahn: Yeah, yeah, a permanent bucket test. And the filtration system, you have to go through the filtration system to get from the float tank to the vat. In that case, like we’re using this whole concept of flow and turnovers to kind of try to statistically figure out how long it takes to get a certain percentage of our liquid to go through the filtration system at least one time. With a system like that you just know if the float tank is empty and the vat is full, all the liquid went through your filtration system to get there. There, really the theoretical and statistical part of it is gone and you don’t really care exactly too much about slightly lower flow because you have a very clear indication that your filtration system is done and it’s all gone through. So in those cases none of this is really as important.

Graham: Although for catching hair and stuff like that still can be useful.

Ashkahn: Yeah, I mean and you can do your routine maintenance but at that point like it’ll just slow the thing down and you’re running slightly longer-

Graham: And hopefully not damage, yeah that’s true, the sanitation-

Ashkahn: It shouldn’t affect the sanitation part of it.

Graham: But, you could be damaging equipment and getting a bunch of hair stuck in your impeller and slowing down a pump more than it wants to and stuff like that.  

Ashkahn: Yeah, but like to the point where I wouldn’t blink an eye at a reservoir tank without a flow meter necessarily. It just doesn’t, it’s not nearly as important as it would be in a recirculation system.

Graham: But would you want in your ideal world to have a flow meter on a reservoir system anyway?

Ashkahn: I guess, I mean, but also you can just know, you know what I mean, like you can just time it back and forth and you’d know what the flow is. The bucket test, you have the bucket test.

Graham: Yes, just do that every morning instead of like glancing at a flow meter say, well yeah, also when you have the flow meters for checking your flow, definitely at least once a day is what I would recommend. Like just go in there in the morning, make sure that the flow is what you expect it to be. Again, if it’s 5 or 10 gallons a minute less, you know something’s wrong. I mean that would be my argument for having it on a …

Ashkahn: Yeah, I mean we check ours because then if something does go weird, we know to fix it right away and we don’t have to deal with slower flow until our six month check in comes or whatever.

Graham: There’s so many tasks to do in the morning. The idea of actually sitting by every one of your reservoir tanks and timing the full cycle to make sure that it’s accurate sounds kind of crazy, like just being able to glance at a flow meter and know it’s getting the right flow.

Ashkahn: I mean sure, it sounds nice, but not completely necessary.

Graham: Cool.

Ashkahn: Okay. If you have other questions-

Graham: Oh, are we done then?

Ashkahn: Is that it, you have more to say?  

Graham: No, I guess not. Yeah. If you have other questions.

Ashkahn: Yeah, go ahead. Go ahead.

Graham: No, you were doing a good job, I didn’t want to interrupt.

Ashkahn: Go to floattanksolutions.com/podcast. And we will answer them.

Graham: Bye everyone.

Latest Blog Posts