Curious "normal" operation for Danfoss valve? Danfoss user feedback request

[jocko]

I have a Danfoss valve that controls water flow into the condenser.  My temperatures on the output of the condenser fluxuates within a band +/- 2 degrees.  I believe this is the Danfoss opening & closing.  I was assuming (perhaps incorrectly) that the Danfoss was proportional - open a valve fractionally not on/off. 

This doesn't impact anything negatively, as I don't yet use my column.  The column dephleg takes the output of the condenser as its input.  Just concerned that when I do start playing with the column that this might cause less predictable results if the input of it's cooling water bounces around in a 4-degree band. 

Thoughts?  Anyone else have a Danfoss and witness this or is my Danfoss not operating normally?

 

[whiskeytango]

My temp stays pretty consistent.  Do you have the bypass valve closed?  In the end of the day its all about how your still is running and not what temp its at. How is your still running? 

 

 

[jocko]

Bypass is closed once output water comes up to temp. 

The still is fine, as I am running it in simple pot still mode.  Once I start using the 4-plate column, I'm thinking it *may* be more of an issue at that time when the input to the dephleg is being used and its input water temp is fluxuating. 

[SlickFloss]

I don't have your specific answer but perhaps this would help the discussion in some way in case someone else doesn't either, I have a reverse acting thermostatic damn foss (;)) that I haven't run here on site but I have played with it a bit, used an FJVA in a different application and (I think) understand somewhat how it works technically:

The ones I have used in a very different application but look identical to the one we have for our future column depgh uses a probe in liquid to modulate the valve, it is not powered. This probe is subjected to pressure changes correlating to temperature changes within where it is suspended (cooling water, vapor stream, effluent, product, etc.). Pressure changes in probe are transferred via capillary tube to water valve. There is a bellows and counter spring controlled by knob inside of the valve. Pressure from the probe actuates the bellows open or closed. When settings are equalized to probe pressure the spindle is held in a way that allows flow, when pressure changes to the bellows the spindle can fall into a position set by the knob where flow will not occur. 

 

[jocko]

@SlickFloss ok, from your description, it seems it's sort of an on/off valve, just mechanical rather than electrical.  Makes sense.  

[Silk City Distillers]

That's a pretty tight band for a mechanical valve.  Oscillation is not uncommon, as the Danfoss does have some lag time (even the one piece FJVA).

The other factor that can influence the oscillation the volume of coolant between the valve and the sensor on the two piece unit.  With slow flow rates, a large condenser, and a long distance on the coolant return tube, you could see lag times of a minute or more.  If you have a temp probe in the condenser, this is going to read exactly like it does on the graph.

Ideally, if using the FJVA, it's should be immediately on the exit fitting of the condenser.  If using the two piece (AVTA or similar), that the probe itself is in the condenser (or immediately after, as close to the exit fitting as possible), and the valve itself as close to the input as possible (which isn't ideal from a user perspective).

Again, that's not bad control, I've seen far worse oscillation on PID controlled proportional control systems.

I can tell you that these valves are proportional, however, that's based on the valve being correctly sized for your flow rates and pressure drop.  If your valve is oversized, or your pressure/flow rates are higher than what is expected, you will get full flow as soon as the valve cracks open - counterproductive if you wanted smooth variable control over the full range.

 

[Southernhighlander]

These valves operate in a proportional manner.  The coolant for the dephlegmator should come from the final condenser. The valve itself should be at the coolant input of the final condenser.  The probe for the valve should be at the output of the final condenser.  You will need a bypass at the valve and at each dephlegmator.  You will need to have some bypass at the valve  to maintain correct functionality throughout the run.

[Golden Beaver Distillery]

2 hours ago, Southernhighlander said:

The valve itself should be at the coolant input of the final condenser. 

Shouldn't the valve be at the output of the final condenser? 

[whiskeytango]

31 minutes ago, Golden Beaver Distillery said:

Shouldn't the valve be at the output of the final condenser? 

I run all mine at the input but Im not totally sure that on the output wouldn't do the same thing.  

 

[Golden Beaver Distillery]

4 hours ago, whiskeytango said:

I run all mine at the input but Im not totally sure that on the output wouldn't do the same thing.  

 

The valve is at input, the probe is at the outflow of the main condenser.

I confused "valve" for "probe".

[jocko]

My Danfoss is installed on the input to final condenser with probe on ouput of final condenser, per the drawing.  It's got the bypass as well, it's  excatly as the drawing.