Pond Boss Forums AERATION Systems questions Valves on rotary vane compressors?

I just installed my new "Loud" gast air pump. It turns out that it doesn't sound quite as loud outside as it did in the house. Anyway, my new pump pushes a lot more air than my older small gast pump. It almost seems too much for my 1/4 acre pond. Are there any negative aspects to adding a valve to the airline to restrict its flow? Would this do damage to a rotary vane compressor?

Do not restrict air flow by using a valve in your air line. If you do this you will wear your vanes out quicker, higher pressure equals shorter life. You will also cause the motor to run hotter and use more electricity. I would avoid resticting the pump any more than necessary.
A better way is to intall a "T" in your plumbing coming from your pump. One branch goes to your aerator, the other branch goes to a ball valve that just vents out to the atmoshere. Then you can crack the valve just enough to bleed some air out of the line going to the aerator. This will actually lower the back pressure on your pump, it will take load off the motor and run it cooler, and it will make the pump last longer rather than shorter. Yes you are wasting some of the air you are pumping but it will actually be less energy waste than if you restrict your air line. You are just pumping some air from atmosphere back to atmosphere. If you don't have one alreay you should have a pressure gauge in the line going between your pump and the "T" I describe. This way you always know what pressure you are running and can tell if it exceeds the manufacturers pump rating.

I have a Thomas vane pump that is designed for a max pressure of 15 psi. I run two aerators with this pump so I have a valve in each line. I use the valves to adjust the flow so both aerators get about equal air. I always leave the one with the highest back pressure wide open and restrict the other one down to even the flow out. When I only have the closest aerator running alone it generates around 9 psi back pressure. When I restict it down to force an equal amount of air to the farthest aerator (valve wide open) I get about 10 psi back pressure. When I shut off the near aerator and only run the farthest one I get about 11 psi. In the summer I run them both (10 psi), in the winter I only run the far one (11 psi). I only run my aerator for two 4 hours shifts daily. Whenever the system kicks on the pressure climbs as the pump is pushing the water out of the air stones and gets high enough to trip the 15 psi pressure relief valve for a few seconds. With this arrangement my vanes have lasted almost 6 years now. I do keep another set handy for the day they crap out.

BZ gives great advice on venting option but you may not need to vent off as that pump is only 2.3 cfm open flow and 1.8 cfm @ 10 psi, What is your diffuser depth and pressure reading.

Thanks BZ. That sounds like a great idea. My diffuser depth is 8', but I don't have a pressure guage on the system. Just as BZ said, when I turned it on, it ran for a couple seconds, then shut off for a couple. This repeated three times until it ran consantly. I have a question about this also. You already said that backpressure will wear the vanes out more quickly. I have a check valve but haven't installed it. Can it be installed near the compressor or does it need to be installed just before the diffuser? One other question: if I do need to install the T and pressure guage, where can I buy this stuff? Thanks again.

If you have the MixAir (some call it soaker hose) type of AirPod it may not have a checkvalve at the diffuser, This is not a good combination for a rotary vane (or any type of compressor)Putting a checkvalve any other place inline with that model of diffuser will not work well either. Having a checkvalve at the pump (intake side) will only keep the pump from running in reverse on startup .Perhaps Cary will wade in on this if your diffuser is an ATI AirPod.Several companies refer to their units as AirPods, My assumption that it is an ATI may not be correct.

Ted, you're exactly right. I just looked at their website and the ATI is the diffuser type that I have.

I'm no expert but I'd think you want a check valve at the diffuser simply because you don't want your pump to have to push a line full of water out every time it starts. I'm not aware that a van compressor can start up in reverse can it? I suppose it depends on what kind of motor is driving it? If the answer is that you don't have too much air going into your pond then by all means don't bleed any off. You can by pressure gauges at most any industrial supply place. If you go to your local Home Depot type place you will find gauges for compressor systems but they usually go up to 150 to 200 psi. You want a low pressure gauge. I found some nice liquid filled gauges for my system at Grainger that range only up to 30 psi. Perfect for this use. You don't want to use a non-filled gauge because the vibration will wear it out in a year or two. Check out grainger.com

Thanks BZ. I got with Ted and he pointed me in the right direction. I have VERY limited knowledge when it comes to compressors so I don't know if a rotary vane pump can run in reverse. Ted previously mentioned that adding a check valve just before my type of diffuser may not work well. Why is this? I'm not questioning anyone, I'm just trying to learn as much as I can.

BZ:

I think if you stop the air from coming out of the line at the top, water will have a very hard time getting into the line at the bottom.

Theo you are correct "if" you could stop air from coming out of the top,(or anywhere else too) any type of compressor/ diffuser system will bleed down in time when it is shut off for a period of time, thus letting water seek its highest level. The systems just dont stay air tight. Where does the air go "dont know" perhaps same place the air in a tire goes that does not leak but loses pressure over time. A back check valve prior to the intake will prevent this from bleeding off quickly,and if the pump is located at or below water level a backflow or syphon back thru the compressor "may" not take place.Seems when starting switches and or start capacitors get weak on rotary vanes they can restart in reverse.We have seen this with power surges and years of operating time and a new capacitor or start switch usually returns the motor to correct direction.For the soaker hose type membranes a check valve at the diffuser is the only place to have them, anywhere else and as BZ comments will have to push the water out of the line.A lot of the checkvalves used are made by Brady and are 3/4 inch and have a rubber o ring on the seat for a seal. These orings do not last long and I think at times do not seal well. I have not found a source for these orings and seldom talk to anyone that uses these check valves that realize the valves should be taken apart yearly to see if the ring is still good, just another item to maintain in this type of situation.The main problem are the organics and calcium that build up on the inside of this type of diffuser, Most vane pumps used in pond aeration are 10 psi models and normally pushing water out of any diffuser will exceed this 10 psi limit, Having a relief valve set at 10 psi in this case will keep the pump from over pressurizing until the water is out of the line.I prefer to have the water on the outside of the diffuser and only normal clean condensate on the inside.Moisture back into the pump either a vane or a piston is what will shorten the life of these pumps along with excessive heat, Keep them dry and cool and any pump should last for many years.

Well there you have it. Pretty well explained. I know that air does leak backward through my vane pump when it's off. You can hear it. Without a check valve the water pushes its way into the line as Ted mentions. One of the reasons I went with the Thomas vane pump is that it is rated for 15 psi continuous. The higher it's rated the longer it should last, I hope! My water must be low in minerals and such since I've yet to have any buildup problems with my air stones or check valves.