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Ive never worked inside one of these little pumps... but I suppose, if a diaphragm had a small leak or a valve was not completely sealing off, it could still seem like pump can still move decent volume if there is no restrictions... (EG - being fed with sap and not needing to draw on it) But building up a vacuum level might not be possible..
I have two lines and two pumps running side by side in the same bush..... The other day, one of them was getting no sap and no vacuum... Turned out that I had a freeze-bust in my little manifold before the pump.. (1st time in 3 or 4 years) .. to quickly eliminate it, I ran the mainline straight to my pump, with a recirc T'd in right before the pump.... Started flowing like a garden hose...
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We're new to these pumps but that may be what is happening. Pumps fine and you can feel the air in the mainline part way up it but it's not pulling the sap from the laterals like our other pump is in the other bush. Also have a new 4008 coming to try a different pump.
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Well we found a combo of issues. Spare diaphragms came in the mail and we swapped it out on this pump. Sap wasn’t really running but we were able get 4” of vac. It was enough for me to hear a leak on one of the laterals- a chainsaw knick by the looks. Connector in and vac came up some more. So I guess these pumps can weaken or deteriorate and still pump good but not generate vacuum. Finicky for sure, need to add a recirc line for next year and see what it will do. For $20 we’ll replace diaphragms at the start of every season and have plenty of spares.
