shurflo question- no vac readings on a no flow day

[Earthman]

Hi all- Little foggy and need a reminder.....got a shurflo pump and am not getting any vac readings at the manifold. Everything is tight, etc. Does it need sap to get any reading at vac gauge?

Thanks,
Mike

[BSD]

Hi all- Little foggy and need a reminder.....got a shurflo pump and am not getting any vac readings at the manifold. Everything is tight, etc. Does it need sap to get any reading at vac gauge?

Thanks,
Mike

yes. the diaphragm isn't powerful enough to suck all the air out of the tubing without sap to prime it.

[Earthman]

Great, thanks for your response. Really appreciated.
Mike

[maple flats]

That's the reason many who use a diaphragm pump design it with a small recirculating line. Then when the flow is slight, the recirculation line keeps the diaphragm wet so it makes better vacuum. That line can be a 3/16 or 5/16 line from the storage tank and it can have a needle valve to slow the recirculation, it takes very little to make the pump work far better.

[Biz]

I usually see 10" of vacuum on my units under no-flow conditions on 3/16" lines, 200 to 600 ft long. If you have longer runs or using larger tubing it can take a while to build up vacuum, but you should see some vacuum even dry with no flow. To prove this, take the pump with inlet or strainer disconnected, power it up and hold your hand over the end - you will feel a good vacuum. Not 30" but probably 10". If you don't see good vacuum, perhaps the pump diaphragm is damaged.

A recirculation helps as Dave says but you must restrict it or it won't work well - 5/16 recirc line is way too big for this size pump unless you add a needle valve or ball valve cracked open slightly. Even 3/16 is too big unless restricted. It doesn't need much liquid to boost vacuum, and too much will cause a drop in vacuum on your sap line.

Dave

[Haynes Forest Products]

These style pumps are liquid pumps and not air pumps. Yes self priming pumps will generate SOME vacuum. The higher vacuum comes when it sucks the liquid from the line creating a higher vacuum. Plus liquid creates a better seal so you will get higher vacuum with liquid present.
Now if you have a glycerin filled valve that was manufactured anywhere else other than your back yard you need to BURP it. You need to take a small instrument and lift the little black rubber fill port on the housing. Now don't go popping it out spilling the liquid all over yourself just open it until it equalizes. I have had my gauge jump 4 points.

[Mark B]

While we are talking about a recirculation line to keep a wet diaphragm, do I have to run that recirculation line back from my tank, or can I plumb it from the outgoing line on the pump back to one of my incoming lines?

[Haynes Forest Products]

Air and liquids take a path of least resistance. If you have a recirculation line you will lower your vacuum at the main line. Now the reason Surflow pumps are so desirable is they can run all day long dry without damage. I would think the only reason to run liquid on a contious basis is because the pump is warn or defective. To me it makes no sense to run a recirc line to try and improve a pump with low sucking ability by lowering the vacuum/suction with a recirc line. To me its like driving as fast as you can to the gas station before you run out of gas.

[RileySugarbush]

Haynes: The recirc helps keep the vacuum level up on these little pumps. I believe it works by helping seal the check valves, and filling the volume of the pump so the diaphragm is pulling on incompressible sap instead of air.

On a day with low flow, there is not enough sap coming down the lines to keep the pump wet and the vac level drops so it takes longer to get the sap flowing out of the trees. The vacuum level is not there. Once things start running you can close it down.

I agree in makes no since to recirculate when the trees are running well since there is plenty running through the pump already, but on those marginal days you can really see the difference when you crack open a needle valve on the recirculation line. It is important to have a restriction ( the needle valve) so the recirculation flow doesn't overload the pump. I put a vacuum gage at the pump so you can dial in the best position for that valve.

[BAP]

Air and liquids take a path of least resistance. If you have a recirculation line you will lower your vacuum at the main line. Now the reason Surflow pumps are so desirable is they can run all day long dry without damage. I would think the only reason to run liquid on a contious basis is because the pump is warn or defective. To me it makes no sense to run a recirc line to try and improve a pump with low sucking ability by lowering the vacuum/suction with a recirc line. To me its like driving as fast as you can to the gas station before you run out of gas.

Shurflo pumps and other diaphragm style pumps will pull higher vacuum if they have liquid constantly running through them. They can run dry, but move liquid better than just plain air. That is why, keeping them wet makes them work better. The re-circulation line does that. The best way to hook up the line is to put it in the tank with a needle valve in the line to fine tune the amount being pulled out of the tank. You only want just enough to keep the pump constantly pumping liquid. I have the Shurflo 4008, and without the re circulation line I was running 10-15" of vacuum. With the line, I pull 20-24" of vacuum on 100 taps. It has nothing to do with the pump being worn or not.