I have a question regarding the bleed line for a SCW. When my HP was installed about a year ago, I discovered my well temps had dropped to the mid 30’s. We determined the bleed line was not working. There is solenoid valve on the bleed line that opens when the well temp reaches 47 degrees. Unfortunately even when the solenoid valve was open no water would flow into the bleed line. The only way to get the system to bleed was partially close a ball valve after the bleed line to apply back pressure on the return line back to the well.
 
                                                    | From HP
                                                    |
                                                    |
                                                    |
           -------Sol. Val. -----(BV)---------| Tee
                       ¾” Bleed Line        |
                                                    |
                                                    |
                                                    |
                                                  (BV) partially closed to force bleed
                                                    |
                                                    |
                                                    |
                                                    | 1” main line back to well
                                                    |
 
I tried re-arranging the plumbing to provide a more direct flow to the bleed line but that didn’t help either.
                                                 Tee
          -------Sol. Val. -----(BV)----------------- From HP
                      ¾” Bleed Line        |
                                                   |
                                                   |
                                                   |
                                                   |
                                                 (BV) partially closed to force bleed
                                                   |
                                                   | 1” main line back to well
                                                   |
 
Any ideas how to plumb this so I don’t have to apply back pressure using the BV on the main line? I would like to set the bleed rate using the BV on the bleed line.

Shorten the line that dumps back into the well. This line is pulling the water downward and creates a negative pressure at the bleed point. But this reduces efficiency the same as the valve does (so I wouldn't do it even if the layout allowed it).

Since bleed only occurs as needed, using another pump to suck the bleed water out makes more sense.

Thanks jonr, the neagative pressure explanation makes sense. What kind of pump would I use on the bleed line? Also there is a vacuum break fitting on the bleed line which allows the water in the bleed line to drain back to the vault. So when the HP is off there is no water in the bleed line. Would a pump still work in this situation? BTW my well is under sized so I'm always bleeding. Currently bleeding at 3gpm.

More details on my WEL page.

http://welserver.com/WEL0167/

I'm not the best guy for an exact pump model. It's what, a little over 0 psi (absolute) to a little over 15 psi (absolute) for a ~15 psi (40') increase at 3gpm? That should be enough to pick a small pump.   You may be able to set the 47F a little lower.

I've been thinking about this bleed issue the last few days. Installing a pump on the bleed line is one option. I just have to figure out how to wire the pump so it only turns on when the bleed solenoid valve is open and the HP is on.

I was reading the MA state SCW guidelines which mentioned the return line back to the well should not allow the water to freefall (cascade) into the well. And the return flow piping shall extend below the estimated low water elevation to minimize the introduction of oxygen into the well water.

I have a hunch my return well line is freefalling into the well. I have ~80' static which I think would explain the negative pressure. I will call the well contractor to confirm. Do you think I'm on the right track? Would this freefall on the return line cause the negative pressure I'm observing?

If I understood you correctly, this will make it worse. To have 80' of water flowing downward in a pipe without causing 0 psi at the top you would have keep your valve in place all the time.

There should be an energy advantage to having the water flow back downward along the walls of the well. Can you seal the well such that oxygen isn't an issue?

Well I'm not actually worried about the introduction of oxygen. I was quoting the reasoning behind the state guideline. I was hoping by extended the return line below the water line in the well. The system might operate more like a closed loop and reduce the negative pressure.

Actually a return line freefalling at the top of the well will not create negative pressure while a return line traveling some distance down the well will do so with the maximum suction occurring at a vertical distance of 32' and equaling about 14.7 p.s.i.

-Adam

OK, then my assumption may be wrong and the well contractor did follow the state guidelines. This would explain the negative pressure. I guess I'll leave the system as is. Functional it's working well and I'm very happy with the cost savings. I'm getting ready to add a second stage solenoid valve and I was trying to reduce the musical ball valves I'll be playing when setting the gpm rates for 1st stage, 2nd stage, with and w/o bleed.

Thanks everyone for the feedback.

I am a scw novice at best, but when it comes to piping.  Could you install a selinoid valve in the location of the ball valve now?  When the temprature valve opens the downstream closes.  A orifice of some type could be used to control the amount of bleed permited back to the well when in the closed position.

I'm not sure what you mean. Replace the ball valve on the main return line with a solenoid valve. Close the main line solenoid value when the bleed solenoid valve is open. Then I would need to add a line after the bleed solenoid valve back to the main line and control the flow via an orifice of some sort. Not sure I understand, what is an orifice device?

Thanks John