OK guys, bear with me here. We've played with pipeline and vacuums for a few years, but never used a releaser. We have Zero brand dairy bulk tanks for our sap tanks in the woods; these bulk tanks were designed to hold a vacuum. We have a vacuum fitting in one hole on top and a manifold for the mainlines in another hole on top. We got a good deal (free) on a 900 gallon SS cheese vat that we want to use for a sap tank, but now we need a releaser device. Cheap is good, free is better. Our evaporator engineer has tested a gravity-based releaser... no moving parts. I'm hoping someone can apply some engineering or experience to his idea, and maybe improve upon it...
Imagine a 3" PVC pipe, about 20'-22' long, mounted vertically inside the bottom half of a 50 gallon drum, with the bottom of the pipe supported 2-3" off the bottom of the drum. The drum would be along the outside of the vat, with an outlet pipe about 2" from the top of the drum running into the vat. The vacuum line from the pump would be connected to the very top of the 3" PVC pipe, with the top totally sealed. 3/4" mainline fittings would be 3-5' down from the top. The extra 3-5' between the sap inlets and vacuum fitting are the safety buffer to help prevent sap from getting into the pump. You run your 3/4" mainlines up to the fittings. He suggests a pinhole at the bottom of the mainlines as they begin to curve upwards in order to allow a small amount of air in to carry up the sap. The way this works is that you start out with the drum full of sap in order to form a seal at the bottom of the PVC pipe. You start the vaccuum and it will draw up some of the sap from the drum and create a vaccuum in the mainlines. Sap will be drawn up the mainlines and into the PVC pipe, increasing the column of sap in the pipe. Eventually, the weight of the growing sap column can no longer be maintained by the vacuum, and gravity will cause some of the sap to be released from the PVC pipe via the 2-3" gap at the bottom. Once the sap level gets to the drain pipe in the drum, it will begin draining into the cheese vat.
My question is not so much a matter of *if* this works, since he already has one of these working at another producer's operation. My question is whether anyone has heard of or seen something like this, and if there is a better design that does not require the high vertical lift. Naturally, a wider PVC pipe will reduce the height required, since the operation is dependent upon the weight of the column of sap. He started with 3" PVC since there apparently is a direct relationship between 1' of 3" PVC = 1" of vacuum.
So, how much sap weight can a vacuum support? If a foot of 3" PVC is required for each inch of vacuum, then can I assume that 1" of vacuum can support 1.5"*1.5"*PI*12"*0.004329 gallons/cubic inch* 8.333 lbs/gallon = 3.06 pounds of liquid? If 17" of vacuum is desired, then the weight of the column will be 17'*3.06 lbs/foot, or 52 lbs at equilibrium? If this is the case, then can I assume that a pipe that is 8" wide would only need to be 6' high (2.86' for the sap column + the 3' safety buffer)? Mr. Wizard, help!!