# [Wet Thumb Forum]-What the heck is wrong with my stupid needle valve



## Doomer (Feb 2, 2003)

I'm using the highly regarded Clippard MNV-4K2 needle valve and I can't get it to hold a steady bubble rate. Seems like it's trying to close on it's own ( bubble rate drastically decreases). About once a week I have to re adjust it. This is the second one to display this behavior and it's got me stumped.

Regulator output is a steady 20 psi. The needle valve is screwed directly into the needle valve using a Clippard 1/4 inch fitting.

Any ideas ?


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## Doomer (Feb 2, 2003)

I'm using the highly regarded Clippard MNV-4K2 needle valve and I can't get it to hold a steady bubble rate. Seems like it's trying to close on it's own ( bubble rate drastically decreases). About once a week I have to re adjust it. This is the second one to display this behavior and it's got me stumped.

Regulator output is a steady 20 psi. The needle valve is screwed directly into the needle valve using a Clippard 1/4 inch fitting.

Any ideas ?


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## BobAlston (Jan 23, 2004)

After you set the valve, do you screw down the "collar ring"?

Bob


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## gsmollin (Feb 3, 2003)

Try returning the CO2 cylinder for another one. I have heard of contamination in the CO2 from bars that don't use check valves. Otherwise, yes, you should tighten the lock nut on the valve shaft.


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## JamesHoftiezer (Feb 2, 2003)

Mine has been holding steady for 4 months now. Once I locked down the collar its hasn't moved a bit.

*James Hoftiezer

Tank Journal - Aquascape ( Latest / Archive )
Tank Journal - Parts and Construction ( Latest / Archive )*


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## Doomer (Feb 2, 2003)

I've tightened the locking collar as hand tight as I can get it. Have thought of using pliers but that shouldn't be necessary.

Never knew contamination could cause something like this. Any way to check if it's contaminated ?


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## gpodio (Feb 4, 2004)

You can also have the tank flushed if that service is available from whoever fills your tank up. I know from other gas uses that moisture can also obstruct needle valves, you never know. I would also check to make sure the regulator is very clean and free of moisture or particles, small particles could be clogging up the needle valve. I've been using that valve on my tank for only a couple of months now but it has held a steady rate so far.

Would increasing the pressure from the regulator be worth trying? Perhaps a little more pressure might help push any impurities through the valve?

Giancarlo Podio


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## Doomer (Feb 2, 2003)

I swap out the empty tank for a full one so getting it flushed wouldn't work. I'll try to turn up the pressure and see what happens. Any idea how high I can safely go ? Don't want to blow my system up.


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## JamesHoftiezer (Feb 2, 2003)

I ahve mine at 30psi with no problems.

*James Hoftiezer

Tank Journal - Aquascape ( Latest / Archive )
Tank Journal - Parts and Construction ( Latest / Archive )*


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## BobAlston (Jan 23, 2004)

If you are going on the theory of something in the valve that is obstructing it, I would suggest opening the valve up to full open for a short period of time. Better disconnect from the tank. Given the diagram of the valve that I recall, that should allow whatever is there to pass. Worth a try as it should be relatively quick.

Bob


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## gsmollin (Feb 3, 2003)

Does this problem coincide with a new tank of CO2? If "yes", then the CO2 is probably the cause.

If there is some contamination in the valve, maybe you can blow it out by disconnecting the outlet hose and opening the valve all the way.

The valve is rated at 150 psi, so pressure is not an issue. The real issue will be if you can control the flow at higher pressures. I had only 10 psi dropped across the valve, and found the flow hard to adjust. If you raise the pressure, then you will have to tighten the valve harder into the seat to control the flow. Under those conditions, the valve may become unstable and shut off completely. What I'm suggesting is that you may want to reduce the pressure so you can open up the valve a little.


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## JamesHoftiezer (Feb 2, 2003)

Is it possible its the regulator that is the issue? Not the needle valve?

The needle valve is a mechanical instrument. If you lock down the collar the valve should not change. On the other hand the regulator has a pressure sensitive element(spring) that can't be locked down in the same manner. 
If the pressure varies it could look like the needle valve but be the regulator.

*James Hoftiezer

Tank Journal - Aquascape ( Latest / Archive )
Tank Journal - Parts and Construction ( Latest / Archive )*


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## Rex Grigg (Jan 22, 2004)

The thought went through my mind that it might be the regulator also. And due to summer coming on the tank pressure goes way up, at least mine does. And it could very well be contamination. I adjust my needle valves maybe once every three months.

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## Doomer (Feb 2, 2003)

Just cranked the pressure up to 30 psi, disconnected the hose from the reactor and opened the needle valve wide open. I didn't see it pass a kidney stone or anything. Guess I'll see what happens.

Rex, do you adjust your needle valve every 3 months because your bubble rate decreases like mine ?

I've got an Aqua Medic regulator on my other tank and I've never had to adjust it.


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## gpodio (Feb 4, 2004)

If the regulator is at fault and the pressure spring is stopping the gas from flowing, wouldn't the low-end pressure dial indicate a significant drop in pressure or completely drop to 0?

You mentioned that you have your tank replaced each time, do many people do this? I'm still on my first CO2 bottle for the tank however I did have it flushed and do not plan on swapping it for a full bottle. One thing I learned from other gas applications is that once the tank drops to 0psi anything can enter the bottle, that's why I always try to have them filled before they hit 0 and always have them refilled rather than swapped. Not sure how important this is for CO2 in aquariums but it is an issue with other, perhaps more delicate appications.

Hope that helps
Giancarlo Podio


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## Doomer (Feb 2, 2003)

The regulator output pressure is rock solid. I flushed the system but it didn't do any good.








I don't have any choice but to swap out the tank. No refillers in my area. Guess I'll have to wait until the next tank to see if it's contamination or not. I have no idea how I could tell unless it settled down when I replace the tank.


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## Rex Grigg (Jan 22, 2004)

The only time I really adjust mine is to change the CO2 values. Mainly when I'm bored.

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## Overfloater (Apr 2, 2004)

Doomer,

I also have a Clippard NV and have been experiencing the same problem since day one. One minute I have one bubble every three seconds, the next the CO2 is coming out at some ridiculously high rate. I have burned through a 5lb tank in 3 weeks and have killed fish because of this problem. My regulator also holds steady pressure. I have noticed that if I push in on the adjustment screw on the NV (even with the collar screwed down), it changes my bubble rate. I am quite frankly tired of messing with it. A fluctuating pH has lead to problems with algae which will never be cured if I can't keep a steady bubble rate. In a few days I'm going to spend the $100 on a JBJ All-In-One regulator setup. It irritates me that I spent $25 on a NV that won't work correctly.


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## Doomer (Feb 2, 2003)

I use a PH controller and, thank God, it mitigates the effects of my erratic needle valve. Everyone sings the praises of the Clippard valve. This is why I went with it when my Noshok turned out to be no good. I'll live with it for now but if I do make a change, it will be to an Aqua Medic regulator/needle valve. I know it works.


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## gpodio (Feb 4, 2004)

I would return the needle valve if that's the case. What was the low pressure set to? Unless there is something wrong with the threads (possible, I recently had a batch of minimatic adaptors which were plated too heavily) it's hard to imagine that once any play has been eliminated by locking down the collar you can still see a difference just by manually pushing down on the needle. I'm sure it's a bad valve if that's the case.

This might sound stupid but seeing it nearly happened to me recently... at +/- 10psi it doesn't take a lot to reduce, stop or interfere with the flow of gas into the tank. A small bend, kink or pressure point can easily throw off your bubble rate. Im my case I noticed the bubble rate had dropped slightly over time, it ended up being the silicon tubing that was slowly getting a kink from a bend it makes behind the tank, it was hard to see if not impossible but I noticed that when I moved the tube around the bubble rate would increase slightly at times so I started looking for it and finally found it. Actually I think it was more of a twist in the tube itself from when I originally set it up.

I haven't tried the JBJ all-in-one regulator, it sure looks like a nice unit and it's ready for a PH controller. Let us know if it fixes the problem.

Giancarlo Podio


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## gsmollin (Feb 3, 2003)

The basic problem here, is that there may not be anything "wrong" with the needle valve. What may be wrong is the application. The Clippard MNV-4 has a specification of Cv=.05. There is also a figure that "suggests" the valve is useful down to Cv=.001. The problem is that our application calls for a Cv=.000002, to get 1 bubble/sec. with 10 psi pressure differential across the valve. The valve is simply not designed to perform this fine a regulation.

To use the valve, we are operating it in the shutoff region. The needle is jammed against the seat, and the flow is controlled by the pressure of the needle against the seat, not its position. This leads to flow instability, and explains why the flow will still fluctuate with the jam nut tightened.

I don't have a fool-proof solution for this, except to perhaps buy a complete system, guaranteed to work in our application. Then if the needle valve is flakey, it becomes the seller's liability. Clippard will not warrant the valve to operate with a Cv=.000002. It's totally at the origin of the curve. Even the Swagelok S is operating off-the-spec-sheet in our application. My S's came with a preset lower limit that corresponded to 5 bubbles/sec. with 10 psi across the valve. I had to remove the limit to reduce the flow rate. I'm happy to report that the S can do the flow control without going into the shutoff region (the S does not have a shutoff region), but it's still being used off-the-spec-sheet.

Godslayer, your problems illustrate the reason I use tandem metering valves. If one of my valves suddenly increases its Cv, then the series valve limits the maximum flowrate change to about 1.5X. (The backpressure of the checkvalve also limits flowrate. I was always worried about that when I was using the single needle valve.

On the other hand, if this is being caused by contamination, no needle or metering valve can fix that. Doomer really needs to try another cylinder of CO2.


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## gpodio (Feb 4, 2004)

gsmollin, I agree with you on the clippard valve not being the best choice, there are needle valves that are better suited but they cost a lot, at least the ones I was told about when I was shopping for needle valves. The MNV-4 is nearly closed in most cases as you said however I doubt this could cause a difference such as the one Godslayer experienced (a bubble every 3 seconds to emptying a 5lb tank in 3 weeks).

I can only speak for my MNV-4 which has been holding a steady rate well so far (knock on wood) however I would love to find a valve with a tighter range at a good price, the MNV-4 can really be tricky to adjust, I'd love to be able to increase my bubble rate at any time, not just when I'm bored and have an hour to kill







Sorry to steal part of your line there Rex but that's exactly what it's like over here too.

Giancarlo Podio


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