Reccommendations On Automatic Draw-Off Units

[rayjavu]

I'd like to know more about your draw-off.

[DrTimPerkins]

A ball-valve between the pan and the autodraw unit is pretty common. The practice mentioned is that you run the evaporator with the ball valve about 3/4 closed most of the time. This will reduce rapid drops in liquid level in the syrup pan and level out the draws considerably by smoothing out the syrup flow from the drawoff valve. It also helps to avoid dropping the liquid level in the pans too much and scorching the rig if you have a huge draw since you can't drop the level below the level of the ball setting. You do need to open it up every now and then (30-60 min) to prevent niter build-up around the valve and if you do need to draw off more syrup than the ball allows at this setting.

It is always good to have some sort of manual open/close either on the autodraw or in addition to it for those occasional moments when you need it.

[rayjavu]

Is it better to use full port ball valves rather than reduced port?

[wiam]

Is it better to use full port ball valves rather than reduced port?

Full port is better. Just in case you need to get syrup out in a hurry. Or when draining pans

[WestfordSugarworks]

I would recommend a modulating auto drawoff. I don't know about what brand to choose but modulating units work better than simple 'open-close' units in my opinion. We have a marcland that just opens and closes and it works fine for us but especially if you are boiling with wood i'd recommend a modulating unit. They help reduce batching when you draw off and you it's more hands-off.

[RIVERWINDS]

I would recommend a modulating auto drawoff. I don't know about what brand to choose but modulating units work better than simple 'open-close' units in my opinion. We have a marcland that just opens and closes and it works fine for us but especially if you are boiling with wood i'd recommend a modulating unit. They help reduce batching when you draw off and you it's more hands-off.

I also have seen the modulating draw offs in action and knowing what I know now, I would have paid the couple hundred extra for a modulating unit instead of getting just an open/close valve. I really would like one now that I'm boiling concentrate.

[Tweegs]

OK…that’s it…dog-gonnit!….you guys….

It bugs me, this flippant use of the word “modulated”.
In my world (electronics, with a heavy emphasis on RF), the term “modulation” wouldn’t normally apply to anything syrup related.
Near and dear to my heart, here is the definition of modulation as I understand it:
https://en.wikipedia.org/wiki/Modulation

A brief look at the above page would leave many a folk scratching their heads, much as I’m doing now but from the other side of the fence.

To get to a syrup related form of modulation as it pertains to auto draw offs, we can define modulation in its most simplistic form, which means “change”.

OK, change what??

I’ve been struggling with the answer to that question for a few years now based on what I’ve read here in different threads.

The first auto draw off I built used a PID controller. There were a few issues with this design, most notably was that niter tended to build up and prevent the valve from closing fully.

It struck me then that “modulating” the valve briefly at the end of a draw (rapidly open and close a few times) would help prevent niter build up. Perhaps this is what was meant by a modulated valve? Some responses in other threads seemed to suggest so.

Version two of my auto draw saw the PID controller land in the trash can, replaced with a micro controller. With the flexibility of writing my own software, not only was I able to modulate the valve, but I could calculate the boiling point of water (given the barometric pressure and altitude) and compensate the draw off temperature based on pressure (with a user offset to fine tune the rig).

Other threads seemed to point to this as the definition of “modulated”. (I’d use the term “pressure compensated” rather than “modulated”. Though it’s technically correct, “modulated” is a very loose fit. Cleaver marketing gimmick, perhaps?)

And now, today, I’m reading that “modulated” refers to something that helps prevent “batching”.
I’m once again confused.

Would someone kindly spell out this form of modulation so that I, and other technocrats, can fully understand what is being discussed?

Thank you!

[rayjavu]

Modulating actuators allow a valve to be opened proportionally rather than just on/off.
From the interwebs:

http://www.engineering-dictionary.org/VALVE,_MODULATING
A valve which can be positioned anywhere between fully on and fully off to proportion the rate of flow in response to a modulating controller (see modulating control).

https://assuredautomation.com/modula...ontrol-valves/
What is Modulating Control?
Many process control valves are quarter-turn on/off valves that rotate 90 degrees from on to off. These are also referred to as stop valves or isolation valves. They are either completely open (90°) or completely closed (0°).
A modulating control valve, however, has the ability to be accurately positioned at any point between 0° and 90° as well. This adds the ability to control the amount of flow in addition to whether there is flow or not.
Quarter-turn valves include ball valves, butterfly valves, and plug valves. All of these can be made into modulating control valves by adding an actuator with modulating capabilities. These actuators can be either electric or pneumatic.
Note: Standard port and full port ball valves do not increase flow evenly in relation to their degree of rotation. There are two methods used to achieve a directly proportional increase of flow with regard to degree of rotation. They are: using a V-port ball, or a trim disc insert.

http://www.ap.emersonprocess.com/en-...odService.aspx
Valve Actuators for Modulating Service
Modulating control valves are used in variable-flow systems in which flow must be adjusted to slow, moderate, or full stream. Due to batch process changes, regulate flow or other control applications, the actuator is adjusted often and its control accuracy of modulating service actuators must remain consistent and not deteriorate.

[DrTimPerkins]

Would someone kindly spell out this form of modulation so that I, and other technocrats, can fully understand what is being discussed?

Two kinds of auto-draw valves. Open/close (solenoid) and modulated. Open/close are simpler and cheaper, and just open when it hits the draw off temperature or above, and close when the temperature falls below. Modulated draw-off valves are motor-driven valves that open a variable amount (typically with a butterfly valve) based upon the syrup temperature input and the programming. Typically if the syrup temperature is right at or just slightly above the set temperature, the valve opens just a tiny amount. If the temperature is further above the set temperature it opens more. Thus the opening of the valve is modulated by and proportional to the temperature of the syrup (the input). I believe the use of the term "modulated" is appropriate in that circumstance.

The terms I have more issue with is "sterile" and "gravity vacuum" or just plain "gravity" tubing. All sap in tubing responds to gravity, not just in 3/16" tubing. Also "vacuum transfer." We aren't moving vacuum....we are moving air. But....I just clench my teeth and nod my head. Sometimes it's easier that way.

[RileySugarbush]

Different industries have there own nomenclature. Sometimes it is a legacy from an old technology.

From the world of motion control, a better term for these more sophisticated draw offs might be "proportional control" Where the valve is opened proportionally to the amount of temperature error. For example, 5% open at the set temperature, and another 20% per degree. The inputs then are set point( initial draw temperature) and gain ( % per degree).

For those that are unfamiliar, the PID controller mentioned by Tweegs stands for Proportional, Integral, Derivative control. The basics for servo control like cruise control on your car.

P is like described above,
I is the amount the valve opens if it has been sitting for a long time at a temp above the set temp
D is how you can get the valve to open more if the temp is rising real fast.