Moisture trap

[DocsMapleSyrup]

Anyone make a moisture trap to protect their vacuum pump? I bought a used Gast rotary vane and will need to either build or buy a moisture trap. Any ideas, photos, comments?

[tcross]

i built one using schedule 40 pvc pipe. i believe it's out of 3" necked down the 1 1/2"? actually i have two of them in succession before my pump. i dont' have a picture so i'll try to explain it. at the top is a 3" to 1 1/2" reducer fitting. (i think it's 1 1/2"... whatever size a racket ball fits into snug). that is where the vacuum comes in. then it's a 3' length of 3" pipe, then a 3" tee, which is reduced to a 1" vacuum line. on the bottom, a reducer to a threaded 3/4" port for a 3/4" ball valve for draining. where the 3" pipe meets the tee, i glued in a wire basket, and put a racket ball in/in it. the racket ball fits the port where the vacuum comes in perfectly creating an airtight seal to avoid disaster. i check the moisture trap drain each time i shut my pump off. usually its dry , but early in the year there tends to be a bit of sap in there due to ice mist being sucked in. i believe my 30 cfm pump is a bit over powered for my hobby releaser. hope that helps. i can get some pictures if i think of it next time i'm in my shack.

[maple flats]

I built 3 over the years. The first one was 3" PVC about 42" long. It was mounted on top of a 1000 gal vacuum tank. I had the 2 main conductors coming into the system 10" up above the tank at a T that was 3x3x1.5". The vacuum came in at the top at a 3x1.25" coupling which then had a 1.25 to 2" ell then to the pump. That proved too small once and sap got to the pump. Then I made another out of 4" PVC, similar design, but this time the sap entered the vacuum tank at one end and this 4" trap and the vacuum pulled from the other end. That way it could only need to stop the vacuum if the tank filled. The time it failed was due to ice and the tank was not full. That second one never failed. That system was about 650 taps using an Alamo 30 and ran at 19" to protect the tank.
At another bush I made one that was 4" PVC 64" tall. That was on an Alamo 75, pulling into a double vertical releaser. One time as things froze, slush formed on one of the releaser dump ports and held the flapper open slightly. Then sap pulled into the moisture trap, iced it up and finally into the pump which also froze solid. It did not ruin the pump but I had to remove the pump and moisture trap, take them home to thaw. I thawed the pump carefully using a weed burner torch and heating the whole pump slowly. On the moisture trap I took it home, put it in the shower and ran the warm shower on it for almost 2 hrs before the ice was out. By the time I got the system back up and running I had lost 6 hrs of sap flow from the time I discovered it was frozen. No guess on what time during the night it had failed.
On my next system I bought a moisture trap (From Ed Sobles) and it never failed. It did stop the vacuum flow twice as the releaser had frozen but moisture never got to the pump. I now shut the pumps off about 2 hrs after the temp is forecast to get to 30F. Then I turn it back on when the temp gets to 34 the next day.
The first 2 described were on an Alamo 30 running at 19". The third was on an Alamo 75 but only running at 17" because that was all I could get with a 6.5 hp Honda. I then bought a 9 HP Honda and set it to run a 23". Each had a racket ball to stop the flow if the trap filled with sap. The last one is at the sugarhouse, using a BB4 on an electric motor and it pulls 26-27" and it has a Sobles trap.
Based on the failures of my homemade traps I will never make one again. Sobles sells them for $800 last I knew.

[DocsMapleSyrup]

tcross
I'd really like to see some photos if you get the chance totake a few. It's a little tough for me to visualize.

maple flats and tcross
Thanks for replying.

[tcross]

yeah, i meant to take a few pics last weekend and totally spaced out on it. i'll get some this week and post them so you can get a better idea.

[maple flats]

I don't have any pictures and I trashed the ones I built years ago, did not keep them. However I can describe how I built the one that worked best. The main body was 4" PVC pipe and 64" tall. On the top I had a reducer that (coupler) was 4" on one end and 1.25" on the other. The trap was mounted vertically. About 12" below that top coupler I had a Wye, it was 4" top and bottom with a 2" facing up 45 degrees out the side. That attached to my releaser, the vacuum supply for the releaser. Out the top I had an elbow, 1.25" to 1.5" which attached to the vac pump. and initially at the bottom I had another coupler, 4" to 2", then a 2x x 1" ell. The 1" had a screw in plug to drain any moisture. After I had a failure (freeze up as sap formed slush in the releaser and when it dumped some slush held the flapper open causing the slush to freeze solid, see reply #3) I changed the bottom to an elbow and flapper (4" x 2" coupler, then 2" x 1.5" ell then a 1.5" 45 and finally a flapper check. Then every time I shut the pump off ( to fuel and check or change the oil) any moisture was dumped. That never failed but I also never had a slush freeze again either. After that I tried to time when the temperature would drop to 30F and try to run out of gas within an hour of that. That approach seemed to work.

[jrgagne99]

I use a vertically-oriented 4" pvc pipe with a raquet ball inside. It sits inline between the releaser and the vacuum pump. Line to vacuum pump is screwed into the top cap, line to releaser is at the side, mid-way up. If the releaser fails and it the trap fills with sap, the raquet ball floats to the top and (hopefully) prevents sap from being sucked into the vacuum. It has a drain valve on the bottom, but I almost never find any liquid inside.

Dave,
I don't understand your system(s). What prevents sap that accumulates and fills the trap from getting sucked into your vacuum pump? You make no mention of a racquet ball or other flow-stopping device?

[maple flats]

Yes, sorry, mine had a racquet ball, I just forgot to mention that. That was the reason for the 1.25" outlet, then back up to larger to be certain the ball did not get sucked thru if I had used a 1.5" fitting. Then it was back up to larger. If a size reduction is short enough it doesn't seem to affect the CFM like a long run does.

[DrTimPerkins]

If a size reduction is short enough it doesn't seem to affect the CFM like a long run does.

CFM is flow of air in a pipe. Flow rate in a pipe (vacuum is just low pressure) is related to radius of the pipe, length of pipe, viscosity of the material (air...not viscous at all), and the pressure. By far the radius has the largest effect however -- in the formula it is to the 4th power of the radius, so you don't want to neck it down too far or too many times.

If you really want to make your brain ache, look up the Reynold's and Bernoulli equations, and the Hagen-Poiseuille Law. Don't say I didn't warn you.

[tcross]

20228

here's a pic of my moisture traps.

[DrTimPerkins]

If anyone is making their own trap, especially if you're pulling higher vacuum levels, it is a good idea to make it so you can open them up enough to be able to remove a stuck ball. They can really get deformed and wedged in the fitting at times.

Note also that if your moisture trap is in one location, but the pump is in another, and there is some distance between them (especially if they're at different temperatures), you can get condensation in the pipe in between them, so plumb them so liquid can flow into them from both directions in that case.

Final hint...a check valve between the pump and the moisture trap is a really good idea. Keeps the vacuum in your system from pulling air (or oil) from the pump back into the tubing system.

[maple flats]

That reminds me, my last one I made (described above) had a T not an ell out the top. The top of the tee had a screw in plug with thread seal, the side out was back up to the larger diameter going to the vacuum pump.
While I had that plug so I could push the ball back down if needed, I never had to do it.

[tcross]

i've always wondered how the ball doesn't get sucked up into the top fittings... however it never has. the bottom 1/3rd of the trap unscrews for such instances. i do have a check valve, however it is between the trap and the releaser... perhaps i ought to move it to the other side? occasionally i get a bit of sap/water in the moisture trap... never more than 1/2 cup worth. i think it's from sucking up ice/ice vapor or my bb4 running 28 " might over powers the releaser form time to time?

[DocsMapleSyrup]

Thanks tcross for the photo. It certainly helped me to visualize what you are talking about.