Shurflo Surging.

[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.

[bmbmkr]

This was my 7th year with 12V diaphragm pumps. All shurflo 4008's now- started with everflo brand, but they just aren't as high quality or as good of a design. This surging, isn't a bad thing, it is usually the different rate of flow from the trees. I noticed it usually first thing when the trees thaw out and start running for the day, or the first day tapping. The replies about multiple lines are correct, but the perceived surging also comes from trees on one line not all producing the same amount of sap as they don't all start running at the exact same time. Each line, even with the same # of taps will have a different output due to each tree putting out more or less sap. I used to watch my pumps and think something was wrong. Aside from having leaks, or a bad diaphragm there's nothing wrong with it. The pump pulls and pulls and even though your gauge isn't consistent, you are applying vacuum to all of your taps. As far as recirculation goes, if your nearest tap is close or even uphill from your pump, the trees push up to 13PSI your diaphragms are goin to get wet pretty quick, and once wet, they will not dry out. The pump is more efficient with liquid than it is with air, but it is still much batter than gravity. With no leaks, and a properly functioning pump, you will absolutely get more sap from taps on a pump than with buckets or bags whether you see it "surging" or not.