rotary vein or rocking piston

Hello Everyone I am a new member but have been reading questions and answers for a couple weeks now. I just bought a property with a 1 acre pond max depth 12 feet accoring to previous owner. I am told the pond has been here 50 years and see alot of muck in the shallows and am starting to look for a an aerator to help clean it up and make the pond healthier. Anyway my question is should I be looking for a rocking piston or rotary vein system.

Thanks
Jim

Hi Jim -
There are tons of posts on the advatages of one over the other - I personally recomend the piston type compressor. We replaced the vane compressors with pistons about 3 years ago and are very happy with the outcome. They require less maintenance, operate at a higher psi, generally are more efficient, depending on what hp, and we have had far fewer warranty claims. We have actually gone to a 2 year warranty on our compressor and components due to the performance.

Sue
Thanks for your input. You must have some level of faith in them because other warranties I have seen are only for one year.

jg74, make sure if you get a rocking piston that it is dual head. Single head rocking piston produces less air than the 1/4 hp rotary vane. Myself, I prefer the rotary vane in your situation of pond depth. Rotary is quieter, and easier & quicker to do the rebuild. If you keep a rotary vane in dry conditions very little annual maintenence is necessary. Most people have problems with rotary compresors due to blatant neglect and allowing occassional moist operating conditions. Operation of rotary for 6-8 hrs a day for 12 ft deep diffuser during the open water season should provide at least 8-10 yrs of service before a rebuild is necessary. Manufacturer of GAST compressors maintains the standard 1 yr warranty. The extended 2 yr warranty is a promotional item from the aerator supplier.

Thanks Bill
My pond is about 25 feet from my house and I could keep it under my deck nice and dry. Should I then keep it in some sort of box to keep it from taking in dust?

Jim

jg74, If at all possible I would put the compressor in the garage, shed or house. It is only a short 25 ft distance to bury an air delivery line to the pond. This will do five things for you. 1. I will insure 100% dry conditions, 2. You will NOT need to build or fabricate a weather shelter, plus pump will have better air circulation for motor cooling. (air circulation & cooling is important for compressors) 3. You will be better able to routinely monitor the operational pressure and periodically (monthly) check on start-up pressurization sequence to see if check valves on diffusers are working okay, 4. garage, shed or house conditions will provide a cleaner air environment for compresssor to operate in, 5. pump will be easier to access than under a deck for checking filters, changing timer, or any other routine maintenence (pump out of sight; out of mind, which makes it easier for neglecting the unit). If you operate pump inside some building, I would not be afraid to warranty the pump for 3-5 years if it was run no more than 10 hr per day during just the open water season.

jg, you are getting a lot of good feedback, I sent you a PM, Ted

This is the compressor I ordered. Again reading up on threads I may set it ip in the garage and run a air line rather then electric to the pond or maybe run both. How big of a line do I need to run since this comp is 1.5 cfm. I assume the cheap black poly tubing is good enough? Will I loose air pressure because of a75 foot tubing run to the pond? I was thinking to run 2 small diffusers. Still havent decided which diffusers or tubing for underwater, still have to think of valves, fittings etc.

ROTARY VANE COMPRESSOR GAST, #1532-P104-G597X. Oil-less rotary vane compressor. Rated at 1.5 cfm. This pump can also be used for vacuum service and is rated 20" Hg max vacuum. Motor input: 115 VAC 60 Hz 0.55 amp, 0.025 hp, 1075 rpm. Single phase. Ball bearing motor. Input and output ports ar 1/8" female NPT. The unit is supplied with a noise suppressing filter screwed into one port and an output filter unit is supplied connected to the other port. The mounting base has 4 flexible shock suppressors installed in the base mounting holes. The suppressor mounting holes ar 3/16" in dia. The centers of the mounting holes ar 3-7/16" apart along the width axis and 2-3/4" apart along the length axis. Capacitor supplied. Dimensions: 5-5/8" long x 4-3/16" wide x 4" high. Stock #PC2050 $39.95

Joey.

From some notes I have in my notebook (but I don't recall the thread I gleaned them from.) Ted/Cary or Sue please correct these figures if they are wrong.

0.16 psi loss / 100' of 1/2" tubing
1 psi / 27" of water depth

I started out with the same compressor in one of my ponds. Fifty feet of 1/2" tubing hooked to one 9" diffuser (0.5mm slits) in 8' of water. Produced a nice boil. Use to run it from 10 p.m to 6 a.m.. At $0.07/kWh cost was about $4.00/month.

This summer I found a surplus store and picked up a GAST compressor, 2.6 cfm(@10psi) 2.4 amps for $34. With handling/shipping $52. Using seperate 1/2" lines (50' each in length) it easily handles two 9" disc diffusers, one is in 8' of water, the other is in 11'. According to the gauge at the compressor I'm running at 5-6 psi. Runtime has been cut to two 2hr periods at night. Cost/month is a little over $4. For the little pond two diffusers is overkill but I'm happy with the 9.0 mg/l D.O. reading I got from a surface water sample taken last month.

Russ,

Right on the money with the psi friction loss and psi required to reach 27" of water.

Joey, I have sent you an email.

Joey where did you order the compressor from?

Here is the page its on, there are a few Gast compressors the one I got is about halfway down. Shipping was 9 or 10 bucks.

http://www.candhsales.biz/cgi-bin/shop991/shop.pl/SID=1811418562/page=REGS.htm#PC2053

Russ,
This may be a dumb question.. the compressor is rated at 1.5 cfm. You mentioned a drop in psi 1.16 give or take plus the loss from the diffuser. I am trying to get a idea of what that means when we are talking cfm. How much cfm will actually get out the diffuser into the pond or is it measured in psi. The compressor dosnt state at what psi it will give 1.5 cfm. I am assuming it will be a rather small amount of air but until I get it and test it I am not getting the picture.

Joey,

What is the length and diameter of the airline from your compressor location to the pond shore?

Then, what is the length, size and depth of the line from the pond shore to the location of the diffuser(s).

What type of diffuser do you plan on using? Do you plan on having multiple diffuser locations or just one?

The drop Russ mentioned was 0.16 Psi/100' of 1/2 " tubing. If you upsize your tubing to 3/4", the pressure loss is only 0.03/100' of tubing.

Trying to keep it simple..

From garage to pond maybe 50-60 feet. I can bury anysize tubing that will be best, so probly bigger then 1/2.

From the shore to where the difusser will go is 50-55 feet if I put one diffuser. If I did 2 then it would be out 50 feet then 10 to 15 each way to right and to left, so 50ft then a tee then 10 to 15 both right and left.

The type of diffuser I still dont know. Hopefully one or two that dont clog and will work. If I go with one diffuser I am thinking it should be bigger, or two smaller if I go that way.

What is the depth of the desired diffuser locations?

Joey,

I'm going to defer all the detailed questions to one of the aeration experts. Cary will no doubt be able to address your questions.

To explain friction loss, in this case pushing air through a tube, I'll use my chickens as an analogy. When my hens try to squeeze out a double yolk egg, THATS friction.

Russ,

If you don't mind, I might use that analogy in the future. That was pretty fowl but better than my McDonalds staw example. Try blowing through a MickeyD straw and then pick up a stirer straw and do the same. The back pressure trying to blow through the smaller straw is very evident.

The depth would be approx 5 feet if I use 1 in the middle, or if I went with 2 it would be more like 4 1/2 and 5 1/2.

The cheap black poly tubing that you referred to above is good enough for your application. It will also be good enough if you replace the compressor with one that has more cfm.

You asked - ""How much cfm will actually get out the diffuser into the pond or is it measured in psi. The compressor dosnt state at what psi it will give 1.5 cfm.""

The Easy answer first: 1.5 cfm factory rating is open unrestricted flow.

Second answer is - air released from the diffuser can be measured as psi and cfm. Air pressure (psi) at the diffuser is mostly determined by the water depth aka head pressure. Secondary pressure increases are caused by reduced size of airline and length of airline. For YOUR listed purposes and distances, the hose diameter (1/2" poly actual ID dia 5/8")and length are mostly academic and insignificant.

A diffuser that has TOO SMALL of pores or TOO FEW pores will cause the pressure and air escape at the diffuser to be greater depending on size of holes and number of pores. Essentially the back pressure or resistance to release air will continue to increase as the holes continue to get smaller and fewer until the extreme situation of no holes/pore for the air to escape and then pressure increases to very high at the pump. Thus the ideal situation, is having a proper pore size and adequate number or pores that do not cause any "measureable" restriction to air flow at the diffuser in or out of the water. Then your only major restriction to air flow will be water depth which as stated earlier is one psi increase per each 27" ( I usu use as convenience 2 ft) of water depth or 0.5psi per foot.

Depending on the capability of the compressor to create psi and amount of air flow (cfm), the general situation is for there to be less cfm air release as the diffuser goes deeper and deeper into water (more head pressure). Compressors from the manufacturer often provide a chart,figure,graph that displays this decrease of air flow as it relates to increased psi.

Provide the water depth at the diffuser and we can estimate your approx cfm based on 1.5cfm and 10psi(10psi is standard for rotary). How big and what shape is your pond? Maybe one diffuser will ultimately produce more water movement than two smaller and lower flow diffusers.

Thanks Bill, I am getting the picture but once that compressor comes I will do a series of small tests so I know what to expect. So far I know I want the compressor in the garage..ok seems like the 1/2 black poly tubing will be fine for the run to the pond, maybe if I want I can go to 3/4. I am getting the black poly will also be ok to run into the pond, whick I will put threw the holes in a few bricks to hold it down. I need a check valve which one I dont know yet, I need a diffuser or two which one I dont know yet. I know its gonna be approx 5 foot deep and I saw a few differnt ways I would like to ancor it prob in a bucket. Like you said I can always change out the compressor and add more cfm if I need it. Here is the layout of the pond. My first thought was to put the diffuser right under where it says 6ft, I kinda would want one where it says new 8 ft but I would be happy with the one by the 6 ft mark or the 2 smaller ones, one to the left of the 6ft mark and one to the right. Trying to keep this simple what would you do?

Ok I think I found what I was looking for. It seems to me that after I get done with the system I should still have approx 1.25 cfm out the difusser. Correct? If you go to the bottom of the page the compressor I ordered is the 1532 series

http://www.gastmfg.com/pdf/rotvane/0532_1032_1532_series.pdf

quoting Joey: I am getting the black poly will also be ok to run into the pond, whick I will put threw the holes in a few bricks to hold it down. I need a check valve which one I dont know yet, I need a diffuser or two which one I dont know yet.

Joey, most diffusers have an internal check valve. Find out before going thru the hassle. I would not run the poly thru the brick holes, or ty-wrap bricks to it. If you use bricks, secure it very well or the compressor vibration will cause pin holes in the line. You may fill old pieces of garden hose with sand and ty-wrap to it instead. Or, slip pieces of rebar inside gardenhose and tie to the poly. For your distance, weighted hose is not too expensive.

Good point about the bricks. The weighted tube is prob a better choice for the pond part. TY

Cary,

Your explanation using the two different straw sizes is a much better example of friction loss but feel free to use the egg analogy as back up. Thanks for posting the psi loss for 3/4" tubing. I'll add that to my notes.

Joey,

When I come out to your site, I will bring examples of different diffusers and tubing with me. I also have a couple of Rotary Vane compressors that I have rebuilt that I can bring but I think the one you purchased will work great.

I will bring parts as well as some AnchorLine weighted tubing to complete the system or show you what you need if you want to do it yourself.

Great post Bill, it helps everyone to see the dynamics of aeration. I sometimes assume everyone knows what I am thinking and don't fully explain the dynamics of aeration.

Joey, I would think about putting one on the other side of the island since the island disurpts the flow pattern in that cove. Just my experence in ponds with islands.

Lastly, if it is okay with you Joey, we can take photos of the system and install to post here after it is done.

Thanks Cary,

The only thing I want to install now will be the tube from the garage to the pond. The rest I want to build in the spring, hopefully haveing the complete plan ready. I want to keep it as simple as possable, as everything I do seems to turm into a big project. I was planning on posting pics when it was done. I know you are right about the diffuser on the otherside of the island, so maybe I will. Just dont want the boils to be to small if I went with 2. After I get the compressor and test it I will get a feel for how it will perform and start gathering things.

Joey - Your estimate of air flow is okay for your application.

Thanks for that link Joey.

I got the pump yesterday. It looks great.. it dont work! I am thinking maybe the capcitor is NG but I will recall tomarrow and see what the company says.. Here we go.. blowing up into a project.

I built and installed most the system I spoke about last year. Thanks Bill Cody for your help. I would have finished it but it started raining, so as it is, it is in but just one difusser. I built the header with 2 valves for each head. Mounted the heads on a creat, you will see in the pics. One patio block for weight in the creat. I mounted the pump in the garage and ran the plastic tubeing to the pond where I put the header. I was continplating if I should put a cooling fan. I ran the system to test it and didnt like how hot the pump got so I tore apart a very old microwave oven, thinking there must be a fan in it, sure enough a perfect specimin.. Anyways here are a few pics when its totally done I will post some finished pics, thanks for everyone advice.

It does give a nice boil. I would say a foot around and the boil is a inch or so high, then it throws bubbles about a 6 foot diamiter. Might be a little light for 2 heads at the same time, well see after I install the second head.

One thing made the job a PIA and I will tell anyone making there own system it can be done, relitivly cheap BUT USE weighted hose. The regular plastic is a PIA to workwith and then to sink it is even worse.