Shurflo Surging.

[vach50]

Second year using a Shurflo 4008 pump to provide vacuum for my four 3/16” lines supporting 100 taps. Everything works fine 90% of the time until the pump loses vacuum. Sap fills the inlet line to the pump and bubbles actually move from the pump inlet back into the sap filling the hose attached to the pump inlet. Sap flow from the pump outlet stops for a couple minutes, then starts again on it own. Last year I called Pentair four times trying everything they could think of before they sent me a new pump. This year same results with this new pump. I’m confident I have no air leaks. Anyone have ideas or similar issues? Thanks.

[DRoseum]

Uneven vacuum in the lines perhaps. I think most of us have seen this when flows may not be consistent across multiple lines - either because of number of taps, elevation drop, location of trees (woods vs open) etc.

One thing I am interested in trying, is adding very low crack pressure check valves on each line. That way small vacuum losses on one line will never affect the others and you won't get backflow at all.

https://www.freshwatersystems.com/pr...pressure-white

0.3 psi is less than 1 ft of water head.

[Hkb82]

A recirculation line solved this issue for me a few years ago. Was having the same issues. It was caused from the air bubbles in the line. If to much at one time entered the manifold it would pause the flow for a short break and then eventually catch up. Would still hold -20 well doing this but not -25.
Once my pressure is built I hold -25 all day heavy flows or slow flows with the recirculation line. You only need a small flow to keep the pump wet at all times. If it’s really flowing you can just close it.

[SeanD]

Another factor is the slope of the line all the way to the pump. If you have even a slight sag or a significant change in slope, that can cause surging. Check out this very good resource Section 14.4 page 243.
https://bpb-us-e1.wpmucdn.com/blogs....-bookmarks.pdf

[vach50]

A recirculation line solved this issue for me a few years ago. Was having the same issues. It was caused from the air bubbles in the line. If to much at one time entered the manifold it would pause the flow for a short break and then eventually catch up. Would still hold -20 well doing this but not -25.
Once my pressure is built I hold -25 all day heavy flows or slow flows with the recirculation line. You only need a small flow to keep the pump wet at all times. If it’s really flowing you can just close it.

Is it easy to adjust the recirculated flow or does it need constant adjustment? Does a simple ball valve work or do you need to fine tuning of a needle valve?

[vach50]

I don’t know much about 5/16” vacuum systems but I don’t think that issue of changing slope at pump suction applies to 3/16” lines?

[Hkb82]

Thanks for adding that link SeanD. Some very good info in that notebook.
My lines have been added to over the years and next year it’s time to redo them and change the configuration a bit. It works well but definitely has room for improvement and also eye appeal.

[Openwater]

Is it easy to adjust the recirculated flow or does it need constant adjustment? Does a simple ball valve work or do you need to fine tuning of a needle valve?

I have a mini stainless ball valve on a 5/16 recirc line (new this year) which doesn't require much adjustment. I usually keep it barely cracked open to pull the best vacuum when sap is flowing. Even when sap is flowing, I found that if I totally close the recirc valve, my vacuum drops slightly; possibly because I don't have many taps going into the pump. It seems each time I check the pump, battery and solar setup, it's usually pulling good vacuum over 25inHg, and the more I fiddle with it, it only drops the vacuum. So I generally leave the recirc valve barely cracked open, unless I'm totally draining the tank; then I close it so it doesn't suck air and lose my vacuum in the lines.

[Hkb82]

My original pump is fitted with a 1/2 pex water line and ball valve that enters the manifold ahead of the lines to the bush. It runs as Openwaters said pretty little adjustment once it’s running. I built a second one last year and tried a needle valve and 1/4 inch line. I had to run it pretty much wide open all the time and could usually only get -22. Switched it to ghe pex and ball valve this year and now it’s running like the other -25 unless I play with it.
The valves are open almost as little as possible most times. Your just trying to keep the pump wet and pulling consistent vacuum. If you get to much air into the pump it will loose vacuum a bit and your lines and system will also loose its equal vacuum Then the pump will have to build equal pressure throughout your lines and system again. If you can prevent this and no leaks you’ll hold -25 vacuum with your shurflo pump. just what I’ve found the past few seasons.

[craigwade2005]

I'll add another recommendation for a recirc line. If you use 3/16 tubing it is small enough that you almost don't even need a valve. I run my needle valve on my 5/16 lines about 1.5 turns open and it's perfect. You'll notice a significant difference.