What temperature do you guys turn off vacuum pump?

[Starting Small]

This is my first year with high vac. I got to thinking how cold does it have to get before you will turn off your vacuum pump? I am assuming there is a rule of thumb. I was thinking sap is not going to freeze at 28-30 degrees since the sap is moving through the lines. Does sap stop flowing from the trees at a lower temp on vac than with buckets? Can sap still flow on vac even if the temps are a few degrees below freezing due to the lower pressure at the taphole?
-Dave

[Brian Ryther]

Turn it off in April.

[500592]

What kind of pump do you have?

[Starting Small]

It is a Delaval 73. Thanks,
-Dave

[shane hickey]

I shut mine off at 20 or under otherwise they're pumping

[spud]

This is my first year with high vac. I got to thinking how cold does it have to get before you will turn off your vacuum pump? I am assuming there is a rule of thumb. I was thinking sap is not going to freeze at 28-30 degrees since the sap is moving through the lines. Does sap stop flowing from the trees at a lower temp on vac than with buckets? Can sap still flow on vac even if the temps are a few degrees below freezing due to the lower pressure at the taphole?
-Dave

Once the sap freezes in the drops and lateral lines there is no real point to having vacuum on. In the morning you should turn on the vacuum before the sap starts running. The vacuum will help break up the frozen sap in the lateral lines faster then if you just wait for the sun to thaw things. The sun will start warming the tubing and the vacuum will draw pieces of frozen sap a little bit at a time down the line and into the mainline. No mainline should ever be froze up so the tubing would be the only thing to thaw out. On my South/East side of the woods I get sap to start running as early as 9:00am some days.

Spud

[wiam]

If you have a manual releaser in a location that freezes you will want to make sure vacuum is off and releaser is empty. Kind off a tight line to walk, but I have found full releaser frozen solid.

[PerryFamily]

Good question, I was wondering the same thing. I have 2 delaval 76 that are gas powered. My plan was to refill the gas at collection, 3pm +/- and they would run out of gas in the night and refilling in the morning upon start up ?

[BreezyHill]

Sap in motion will need a slightly lower temp to freeze at than sap not in motion. The temp to shut down at is variable from bush to bush. Factors that play into the temp include, but are not limited to: tubing used, connectors, bush elevation, valleys, slope of the tubing, prevailing wind, elevation, density of the trees in the bush, etc

the thicker the tubing the higher its insulative value to keep the sap flowing
plastic connections have less of a convective property and will stay warmer longer
heat rises and cold will settle in the valleys and low areas on a calm evening
the greater the slope to more energy in the sap and the lower the temp is needed to freeze the flow
the more closely spaced a bush is the longer it takes for the cool air to settle in suck the heat out of the sap in the tubing

For my location it varies on which side of the sugar house the bush is located. On the north side is a brook that the mains cross. At 27 degrees the mains slush that cross the brook; while the mains on the top of the brook will still be flowing. The bush will still be flowing but this is typically only for another 30-45 minutes.
On a windy day the temp is usually only at 30 degrees for everything to freeze.
Wind from the south freezes the south bush well before the north bush, as the south bush is above the north bush's elevation.

If you are looking to set a aquastat for a single temp I would say 26. This should give sufficient time for the mains to empty into a releaser and the 5/16 tubing will have frozen solid.

Setting the temp to high will risk damage/ ice filling a releaser; while too low is a possible waste of $$$. BUT there are those of the camp that feel that running the vac on 24/7 is beneficial as there is less of a chance of sap getting back into the tap hole when things start to thaw in the am. There are also those that feel that running high vac on empty tubing creates leaks. So I set at 27 degrees because this is my typical freeze point and it is my on temp, due to the drops on the southeast side of the trees will start to thaw with the morning sun prior to 32 degrees; thus limiting the possibility of sap returning to the tap hole that is in the drops.

As for the pressure affecting the freezing point of sap I have not tested this but a chemistry teacher tells me it will have only a tiny affect if any noticeable difference.

I would like to hear if Dr Tim has found a dif in freeze/thaw point of sap under high vac, 20" vac and no vac.

Ben

[DrTimPerkins]

I would like to hear if Dr Tim has found a dif in freeze/thaw point of sap under high vac, 20" vac and no vac.

As you say, there are several variables, so it isn't possible to set one temp for all locations and have it be right all the time. Amount of flow, size of tubing, how fast the temperature is dropping and leaks will all have an effect. The main difference due to vacuum level (your question) will be due to leaks. The higher the vacuum with a given leak size, the higher the temperature the sap will freeze at.

[rayi]

For those of us that have a glass reciever/bender what happens when the sap freezes in it.

[BreezyHill]

Say good by to your little friend. The freezing in glass is at a minimum a pain to slowly heat with a hair drier...don't use torch as it will likely shatter the glass. At worse the glass will be broken. My new system employs a glass delaval releaser jar. It will be set up so that all liquid will leave the jar on vac off. Any sap that flows in on gravity will drain to the collection tank below. It is inside so it is protected somewhat from environmental changes. It is Pyrex so it is stronger than non pyrex glass; but I have seen them shatter from a relatively small impact of a milker unit that was kicked off a cow. The positioning of a heat lamp on the unit with a thermo control is good insurance.

[Maple Hill]

[QUOTE=PerryFamily;234458 My plan was to refill the gas at collection, 3pm +/- and they would run out of gas in the night and refilling in the morning upon start up ?[/QUOTE]

Thats what I did last year and it worked out fine.

[rayi]

OK Breezy Hill any pics of how you do that

[red maples]

Shut it off when everything freezes up!!!

the only time that I turn it off early is if you have a very windy day that starts warm and then the temp drop Very quicky I have had the 90* elbow and flap froze under the manifold and things backed up and created a mess!!! but that's it. talking a drop like 40* to 20* in a matter of an hour it seemed like very weird it only happened once.