tight valve knob

[stepfen]

Hello everybody,

I have a tank valve that has quite tight knob. In February 2020 I serviced it (total rebuild) myself. After the service the knob was still tight but doable. BTW I used more than "just shiny" tribolube around the threads of the seat assembly by not too much (this thing is expensive after all).

Due to the lockdown since February I have done "only" 6 dives with it but the knob has already become too tight! I can still operate it but quite a bit of force is needed. Am I doing something wrong???

After the dives I just rinse the tank/valve with a garden hose few times. Sea water shouldn't enter the internal parts of the valve anyway.

Here is a picture of the valve:

It is very similar (if not the same) to Polaris valves that are quite common here in Europe.
As you can see the knob itself is quite small (not the usual long and wide knob) and that doesn't help either.

FYI it is the type that takes this kind of service kit:

In contrast I have another valve made by S.O.S. and I can turn it with just the tip of my finger.

The obvious solution would be to buy a new valve, but budget is very limited due to the situation.
Any other solution?

Thanks a lot

 

[Scared Silly]

Could be an issue with the chrome plating and the tolerance making it tight.

 

[stepfen]

The internal parts of the valve body were in very good condition - like new.

 

[halocline]

Is it only tight when there's significant pressure in the tank, or is it still hard to turn with an empty tank?

 

[stepfen]

Is it only tight when there's significant pressure in the tank, or is it still hard to turn with an empty tank?

Hmmm. Don't remember that. Now the tank is full (200bar) and it is definitely hard. I plan to dive it on Wednesday and I will report back.
What would it mean if it is hard only when full?

 

[Angelo Farina]

Hmmm. Don't remember that. Now the tank is full (200bar) and it is definitely hard. I plan to dive it on Wednesday and I will report back.
What would it mean if it is hard only when full?

It means that the O-ring and the white gasket are to be swapped. With high pressure, the O-ring pushes against the white gasket. Being open, it tends to expand, making the knob hard to rotate...

 

[johndiver999]

After the dive, I would take the valve apart again and look at the threaded seat piece. Check the threads on that. I might brush them hard, make sure they are nice and then lube that threaded area. I doubt the tightness is associated with the valve stem, especially if it is new and recently replaced and lubed. You will be able to see if that is the cause when you remove the seat.

When my valves get tight, I always try to lube the threaded section that is screwing in and out.

 

[rjack321]

There should be a Teflon ring on the outside of the valve stem under the bonnet nut. Where the red mark is

 

[johndiver999]

. good catch.

 

[stepfen]

It means that the O-ring and the white gasket are to be swapped. With high pressure, the O-ring pushes against the white gasket. Being open, it tends to expand, making the knob hard to rotate...

Good point and although it makes sense I hesitate to interchange them. The picture of the stem is how it came out of the valve when I first opened it (and I am pretty sure it was the first time it was dissembled since it left the factory). Also all the pictures I can find on-line (eg google) have the stem as shown here. Finally in the book "scuba regulator maintenance and repair" Vance Harlow describes it as: "The o-ring goes on first, so the washer is on the outside of the stem". Kind of vague but I assume that by "outside of the stem" he means the low pressure side i.e. as I have it.

There should be a Teflon ring on the outside of the valve stem under the bonnet nut. Where the red mark is

The said teflon ring is not shown here because it goes inside the bonnet nut. I think its' purpose is to prevent metal to metal contact when the valve is fully open (BTW I think that this is somewhat related to the famous quarter turn that can kill the diver)

After the dive, I would take the valve apart again and look at the threaded seat piece. Check the threads on that. I might brush them hard, make sure they are nice and then lube that threaded area. I doubt the tightness is associated with the valve stem, especially if it is new and recently replaced and lubed. You will be able to see if that is the cause when you remove the seat.
When my valves get tight, I always try to lube the threaded section that is screwing in and out.

First I will remove, inspect and lube the stem (much easier as it can be done even with the tank full). If that doesn't help I will then have a look at the seat. If all these fail, I will have to try @halocline 's and @Angelo Farina 's suggestion (have the washer on the high pressure side of the stem o-ring). I am a bit skeptic about this, because I don't know if this will have any side effects.

Thanks a lot