Chosing the right needle valve

[lurklaban]

Hi all!

We're running a CM machine and for control of reflux condenser water flow a needle valve was purchased. However, it turned out not to bee as easy to adjust as hoped - of the 1 and 3/4 turns available on the valve, less than 1/4 of a turn was used (that is, from closed to full reflux, less than 1/4 of a turn was needed leading to Verry sensitive adjustments where you really wasn't sure if you had moved the turning wheel at all but still sometimes could make quite a big difference in output)

Now my naive brain thought that since the current needle valve was 10 mm (about 3/8 inch), a needle valve of 1/8 inch would give about 1/9 of the cross-sectional area and hence make the available range for adjustment greater. A needle valve of 1/8 inch was ordered from Aliexpress, but - to my great dissapointment - the results was still quite the same as with the 10 mm valve.

Any sugestions on what's wrong and how to know what needle valve to use or if there is another way to make the adjustments less sensitiv? (We did lower the pressure from the water outlet from 2kg to 1 kg and it made some difference, but not much...

Regards
LurkLaban

[Saltbush Bill]

Without going to the shed and counting turns I can't be exact, but I would estimate that all of my needle valves have at least 4 turns in them.
Even then the difference between not enough flow and to much is fairly small, a small part of a turn.
CM's are finicky when it comes to water volume, just the nature of the beast......and why we recommended needle valves to begin with.
Mine range from the biggest stainless one which cost about $120.00 12 to 13 years ago through to 3 x brass cheapy's that were about $22 each.
The cheap ones do just as well as the expensive one imo.
That could well depend on brand name /manufacturer though.
Pretty sure my big one has about 6 turns in it from full open to full shut, that does not mean the same amount of turns from full reflux to a good product take of speed.
I'm not sure that water pressure makes that much difference , most needle valves are made to control flow very accurately at extremely high pressures such as in hydrolics.
I think my big one is rated at 4000psi from memory.

[Stump Lake]

I run a CM still also. My original reflux needle valve is very touchy. Sometimes a 1/8 turn was needed to get it just right.
I tried to get better control by adding this Garosa 0.1 - 0.5 GPM Flowmeter. It helps but it is not the cure I thought it would be. I like that the control knob gives me a lot more turns for a little change in water flow.This is good.
The little red flow float thingy is useless. My water has a lot of air in it. The air comes out of solution in the Flowmeter and sticks to the red float and gives inaccurate readings. I have a small rubber hammer that i keep tapping it with to get the air bubbles off of the red float.
I'm going to leave it on until I come up with something better. I do like having more control in turning the valve knob.

[Swedish Pride]

Looks like its plumbed to the inlet, change it to the outlet.
I found it very finickity until I swapped it around

[Yummyrum]

I also did the needle valve on my 4” plater . Combined with a Three way valve to allow , no reflux , full reflux or Via needle valve ( controlled reflux )

Mine also had around 5 turns but critical zone was around the 1/4 - 1/2 turn region . In my case , pressure was reasonably low …. A 350w sump pump ( I think some call then Butt Pumps )

I think there is a song that goes “ some things will never change , some things remain the same “ ………… or some shit like that

And for the record . Bad pics but there are three connection points in that deflag . There are two on the bottom and one at the top .

One of the bottom ones is not connected and is just an anchor point fir the valve cluster .

[Stump Lake]

Looks like its plumbed to the inlet, change it to the outlet.
I found it very finickity until I swapped it around

I do have it plumbed to the inlet. I thought that is where it should go. I will move it to the outlet on my next run and see how that works.

Thanks

[Yummyrum]

Inlet or outlet .

Top or bottom ?

In my experience you are best to have water enter the bottom and exit the top . Where you stick the valve makes little difference .

I know this goes against Counter flow convention , but unless you loop the outlet higher than the inlet , you’ll have a “dry” deflag unless you stick the valve on the outlet .

[Stump Lake]

unless you loop the outlet higher than the inlet , you’ll have a “dry” deflag unless you stick the valve on the outlet

I'll keep my inlet water coming in the bottom of the defrag and my outlet water going out the top of the the defrag. I think I will try moving the valve to the outlet side just to see what it will do.

air comes out of solution in the Flowmeter and sticks to the red float and gives inaccurate reading

I'm wondering if this might help my air bubble problem. It's not a hard change. If it doesn't help I can always move it back.

[airhill]

Water pressure does make a difference although the taper of the needle contributes quite a lot.

Aside from everything else perhaps you should make your knob more accurate.
A number of years ago I had a bok, it didnt have a needle valve but instead a small ball valve it was a pig to control I ended up flattening the end of a 2' length of copper pipe and slipping it over the tiny handle. Yes it looked a bit funny but I could make very small adjustments, I can't imagine it would be hard to modify the knob on the needle valve.

[shadylane]

I used a needle valve from an old Freon recharger. The kind that screws onto a can.
I soldered the hole shut and redrilled it to a smaller size and ground a sharper taper on the needle.
The valve has 8 turns from seated to wide open, The usable range is less than 1 turn from off the seat.
Before the mods, it's usable range was around a quarter turn.