Shurflo shortcomings and how to overcome them

[RileySugarbush]

As do many others, I have been using a Shurflo diaphragm pump as a vacuum booster on the lower end of a 3/16 gravity setup. In my bush, some of my trees are low on the slope and therefore don’t get much help from the natural vacuum. In fact, on some lines with a low slope at the bottom, there may be a back pressure on high flow days due to the higher flow friction of the small tubing. The Shurflo helps by drawing a vacuum on the bottom sections. But I have been disappointed with how the pumps work when there is a high percentage of air in the lines, either due to low flow conditions, small leaks in the line/taps or tree outgassing. The pumps just don’t draw well when there is air in the lines, resulting in vacuum at the pump of only 10 to 15 inches of Hg. This happens at the worst possible times, when you want to get the flow started and fill the lines after a freeze or when there is a general low flow condition. Adding a recirculation line to keep some sap on the pump inlet certainly helps, but the pump still doesn’t pull very good vacuum when there is any air present, at least for me.


I’ve been trying to solve that problem, and have come up with something. I have added an additional vacuum source to suck out the air and a separator so that the Shurflo only pumps sap.


For a vacuum source, I used a venturi vacuum generator, driven by water. These devices are normally driven with compressed air, requiring a lot of air flow and therefore a big compressor. I chose instead to drive it with a cheap shallow well pump recirculating water from a tank. The venturi gives a steady vacuum of 24 to 25”Hg pulling on liquid or gas. By connecting the vacuum port to a tall chamber made of PVC pipe, and connecting that pipe to the sap lines, gravity separates the gas from the lines and the sap, with the sap going to the bottom and the gas staying on top. It turns out that when a Shurflo is drawing only liquid, it can pull the sap out even against the high vacuum. If the pump gets ahead of the sap flow, it stops pumping and a check valve on the output prevents any back flow. No releaser required, the Shurflo provides that function.




The contraption works!


In this installation, I am using a 1/2 HP shallow well pump ($110 on sale at Fleet Farm), a Vaccon JS-300 vacuum generator ($184 new, but you can find them used cheaper on Ebay) , a 35 gallon tank to hold the water ( had it already) , a 48” length of 3” PVC as the vacuum chamber( $12 with caps) and a 12VDC Shurflo 4008 to pull the sap out of the bottom (had it). Misc. pipe, tubing and fittings fill out the bill of materials.




I have run it for a couple days straight, and it pulls at least 24” on 4 lines with a total of 60 taps, in low flow conditions with lots of air, empty lines, or high flow with mostly sap. I think I could possibly double the number of taps on the system as it is, but that would need to be tested.


This has dramatically increased sap production on these lines, keeping them running when all my open taps with sacks have stopped.

[mellondome]

You could also do the same with a cheap a/c vac to remove the air. ( less hp required) What you have is essentially an electric releaser.

How are you keeping the water from freezing ? What drove you to use this route to create your vacuum?

[RileySugarbush]

A cheap vacuum pump might work, but may not have the capacity and I’m not sure how long it would last at high vacuum and 24 hour operation. I was originally going to suck both sap and bubbles directly out of tubing into the Venturi and then the tank, using sap as the working fluid. That would have been perfect, with no shurflo needed and no separator. But as usual, there are problems!
The cheap cast iron pump would be fine for a single pass (not selling this syrup!) but recirculating results in rust colored sap. Unacceptable. Worse was the fact that the working fluid heats up when run through the pump repeatedly. Ok for water, not so good for sap. That answers your question about freezing. The water gets warm and never mixes with the sap.

So this isn’t a solution for a big vac system but works here. Robust and relatively cheap.

Best of all, fun to figure out and watch run.

[maple flats]

Before you go to all of that extra expense, have you tried just having a small loop bringing sap back thru the Sureflo pump? That is very effective for many who use the diaphragm pumps. It help just by keeping the diaphragm wet. While a diaphragm pump will move air, it does not move very much if the diaphragm is dry.
My only diaphragm pump is on my water heater. It draws water from about 14' of 1" tubing, then about 7' of 5/8" tubing. The tubing starts about 5' lower than the pump. At day's end I drain those tubings to keep them from freezing so to start it flowing the next time I am pumping with a dry diaphragm. I first open the supply tank valve, which has a water level higher than the pump so there is a head of pressure. Even with that the pump takes 45-60 seconds to pull the water to it, but as soon as the first water reaches the pump I get 3 gpm+ water flow.
My point is, just try a recirculation loop out of 3/16 tubing, and if your infeed is only a single 3/16 line add a valve in the recirculation loop to lessen the flow thru it. You only need enough to keep the diaphragm wet. If your infeed for the pump is a manifold bringing several lines in, you likely do not need a valve in the recirculate loop.

[RileySugarbush]

Thanks Dave. I had a recirculation line with a needle valve on my Shurflo for the last two years and it does help. Pulling on empty lines without recirculation results in less than 10”. Adding the recirc boosts that to over 15. Nice. But not a steady vacuum and nowhere near the rock steady 24/25” I’m getting now. Similar results on lines with air bubbles. Reducing the percentage of air by adding more sap that way helps. Eliminating the bubbles, with this separator and my convoluted vacuum generator or some other vacuum pump (as mellondrome suggests) makes for a huge improvement.

I’ll run a comparison this week.

[jmayerl]

Let me just say that it's always good when you figure out something that works well for you, but you have extremely over complicated things for yourself. I run a shurflo on 3/16 with 225 taps that pulls 25-26" and another on 3/16 with 75 that pulls 29" all day. The key point in making a shurflo work the best is having the correct slope on the incoming line so that it is a smooth flow of sap and air. I have manifolds that connect all the incoming lines then a short piece of 1/2" line sloped into the pump. The pumps will work great if setup like that.

[jmayerl]

https://youtu.be/3ihDBd5VVik
Here is the 75 tap set up on a moderate flow

[RedMapleCreek]

It's odd that you were only able to get 15" of vacuum on a Shurflo with a recirc line. You may have had some small leaks that would affect the lower volume Shurflo more than it does the likely higher volume vacuum setup you created. I have two 3/16 lines, each with 24 taps and 600-700 ft long, coming into a 4008 Shurflo. I routinely get 25-26" of vacuum using a recirc line with a needle valve adjusted for maximum vacuum. I have seen many others on this forum also report getting this high level of vacuum using Shurflos with recirc lines.

[RileySugarbush]

Jeff,

I have seen you mention that you get that high a vacuum but I have never been able to replicate it. My setup is almost the same, with a manifold combining 4 lines, a recirculation line and a feed to the pump. I've tipped the manifold to change the angles and all, but when there are any significant air bubbles in the lines the best I can consistently achieve is between 15 and 20 inches at the manifold. Gravity gives me much more at the top of course, but my lower trees don't see that. If I can keep it simple like that I will switch back!

I'll try to replicate your setup neatly exactly and see if it works for me as well. Do you get that kind of vacuum in marginal flow conditions when the trees would not be flowing under gravity alone and the lines are near dry, just by a recirculation line?

[RileySugarbush]

It's odd that you were only able to get 15" of vacuum on a Shurflo with a recirc line. You may have had some small leaks that would affect the lower volume Shurflo more than it does the likely higher volume vacuum setup you created. I have two 3/16 lines, each with 24 taps and 600-700 ft long, coming into a 4008 Shurflo. I routinely get 25-26" of vacuum using a recirc line with a needle valve adjusted for maximum vacuum. I have seen many others on this forum also report getting this high level of vacuum using Shurflos with recirc lines.

Maybe I have a leaky system or particularly gassy trees!