Aviation Gas

[ER_Azza]

Hi

Working at the fuel terminal, I encounter ball valve issue. It gets pretty tight (only jerky motion) when trying to operate it.
(The ball valve is after the tank skin gate valve and strainer)

It gets harder to operate over time.
Had to replace the valve every two to three years it seems.

My query is the material .
The ball valve has a CGPTFE seat & Viton O-ring
I wonder if there is any other alternative material for used on Aviation Gas fuel.

Thanks in advance

 

[3DDave]

Is the ball still mirror smooth? Have you looked at the shaft and shaft seals?

The seal materials you mention are typically used for this application.

It could be that the CGPTFE is getting the graphite mechanically worn from the surface and you are seeing a higher friction on the remaining PTFE. Is this a high use valve? It's seeing 2 strokes (open and close) per use. Making up some numbers - 20 times a day, 7 days a week, 365 days a year for 3 years is 300,000 actuations, which is a lot, but your use may be less?

**Edited - my recollection is right, however the water/air effect in graphite was later proved wrong.

 

[PeterIgg]

If you can give some more details it would assist:
Size?
Class?
Floating/trunnion?
I assume it is just under natural head pressure from your description. How much head?
Did you do any examination of the previous valves removed from service? Did you notice swollen eastomers/seals that lead you to this concern?
When operated, is the valve left in the fully open or closed postion? Soft seated ball valves do not perform well when used for throttling or left for long periods of time in a partially open position.

 

[ER_Azza]

Hi All

It is Trunnion ball Valve. With actuator attached.
CL150, 6". When disconnected/engage actuator still working.
Manual operation of the valve becomes very hard over time.
Valve operate full open or full close. Average of twice a day - to open and to close.
Natural head of the tank to a pump suction for transfer to a tank truck.

I've only heard about the history of the valve recently since joining the company.
Have not got a chance to strip and investigate the valve. Will do when replaced.
But I hope not replacing like for like - and will encounter the same issue in the short run.

 

[LittleInch]

Any diagrams of the valve?

What is trunnion bearing material?

Manual operator type? - Gear or bar?

It does sound like one of the elastomers is hardening under exposure to aviation gasoline. Have you asked the valve vendor what is excellent instead of good?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bcd]

There should be no compatibility issues with the fuel and seat material.

First thing that comes to mind is that a Viton o-ring seal requires lubrication for assembly and cycle life. The fuel could be dissolving the grease, increasing wear and friction. But since the stem seal is close the the axis of rotation, it does not have as large an effect on torque as the seat and trunnion bearings. So my first focus would be on the trunnion bearings. What material are they and how long do they last? Some of the cheap bearing materials will only last a few thousand cycles at best, and may not be compatible with the fuel.

The second thing to look at is seat design. Is it a spring loaded seat or a cavity relief type seat? Or is it a block of Filled PTFE that is jammed into the assembly. The jam type seat usually need a lot of grease to minimize friction. If the fuel dissolves the grease, then the torque will rise significantly.

These are the most likely reasons for the torque increase over time.

 

[gerhardl]

Like others: first suspicion is the sealing materials and sealing geometry and mechanical and chemical wear and additionally abrational wear over time. But why CGPTFE? Would PTFE be better?? No obvious chemical reason for failing elastomers, but additives might be? Delrin and Kalrez (Europe) are higher priced alternatives.

Another ting by actuators is the precise adjustment of limit and torque switches. An updated system for electronical registration and control of actuator movement might add to knowledge and precisison.

 

[ER_Azza]

Hi All

I aviation gas being a "dry" fluid, I suspect it is affecting the seal & potentially the seat.
CG-PTFE, first time I encounter this specific product.
Unfortunately, the valve specifications for this company is not as comprehensive. Pretty much the same across for many fuel type.

I have attached GA drawing.

 

[LittleInch]

There are two injection points. Do you or can you inject grease into them?

If I've read this right there is a bearing surface also on the top of the ball?

Can you attach the drawing as it is difficult to read the fine details when you post in images.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[PeterIgg]

I would tend to agree with BCD, the material selection should be suitable for the application unless there is some peculiar additive in the fuel. One of the causes for increasing operational torque in trunnion mounted ball valves is the acculuation of foreign matter betweent the back of the seat carrier (04) and the body/tail piece (02), or in the body cavity itself (i.e. between the two seats where the ball sits). If the seats cannot move, piston-like, on and off the ball, the friction between the seat and the ball will steadily increase, with a commensurate increase in the required torque to operate. I apprecaite that you metion a strainer in the system, but even a fine silt can cause this issue over sufficient time.
With respect ot LittleInch's comment, there are specific valve seat lubricants on the market that are designed to be injected into the seat seal area through the Energency Seat Sealant ports, but I would rule the issue of jammed seats out before going down that route. Irrespective, I would use these before a generic grease.

 

[LittleInch]

Good advise above. The shaft injection points are first for sure to try, but if all you're doing is replacing the valve and not trying to dismantle it to see whether you can clean it or see where wear is happening then there are many potential areas here that could be the cause. The bearing surfaces seem to be "Du dry" ? what is this?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bcd]

I'm pretty certain this is the problem. The valve has DU trunnion bearings. DU are metal backed bearings with a bronze, PTFE and lead liner. They are made by Garlock. In this design, the bearings are rather small relative to the pressure force they need to carry. They are not going to last very many cycles. Once the upper trunnion bearing wears, pressure force will side load the stem and it will start to gall against the bore it is turning in. Galling will give you the jerky motion you are observing.