Pressure Cast Valve Wear 1

[MntReliabilityEng]

Hey everyone,

I am working on a pressure cast system that is running highly abrasive pottery slip and valves are failing on a biweekly basis.
Here is a simple drawing of one of the 20 stems on the system:

We are currently running 3/4" actuated ball valves with reinforced Teflon seats made by Bi-Torq for both the fill and drain. The system starts by building 160psi, the fill valve opens, and injects the slip into the mold. After the mold is cast, the fill valve closes and the drain valve opens to atmospheric pressure. Its good to note that these ball valves are not used as flow controllers so its either 100% open or 100% closed. The problem we are having seems to be attributed to the drain valves opening under full pressure to ATM. The valve seats are eroding and the slip is able to bypass during the fill cycle causing a loss of pressure. I have theorized a few ways to reduce the amount of wear but I am not an expert so I figured I would come here for advice. My thought is that they could switch from 3/4" to a 1" ball valve in that section to create an expansion chamber which would slow the flow velocity past the valve by 44% while maintaining the same flow rate. They have also considered switching to a ceramic ball and valve seat but its not offered by Bi-Torq so we might need to use a different actuator. I have even looked into switching to a pneumatic actuated gate/knife valve but I don't know if that would be any better. What are your thoughts?

Joe-

 

[Allen555]

It is impossible for gate valve to 100% closed.

 

[Danlap]

Hi Joe,

I am not a process expert, but your schema is way too simple.
Assume ball valves used are floaters. It is not advisable to Operate single barrier valve (the drain valve) with full differential pressure condition.
Ball pushed by the pressure against the downstream seat. And whether its dirty or not, the full DP will increase friction to rotate the ball. And you know the rest, Seat normally the 'softer' part shall compared to Ball.
Not really sure whether your system constrained by Cv: 3/4" Ball valve Cv range from 15-32 and for 1" Ball Cv range from 28-60. Does it really matter? its yours to decide.
Suggest to reduce the Delta P borne by the Drain valve. Maybe, just maybe replace it with Double Block and Bleed. Or add other valve downstream of the drain, and between those two valves, add some tubing/drain line to the downstream (to initiate pressure 'equalization').
Or maybe replace the Drain ball valve with two gate valve (to compensate leakage rate as Allen 555 mention above) or globe valve

The BTO (Break Torque Open) and BTC are normally the highest value. In fully close position, its not velocity that push the Ball but the pressure. By that respect I presume replacing 3/4" to 1" will have the same result as yours problem currently.

Regards,
MR

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

 

[MntReliabilityEng]

MR,

Thank you, your post was very helpful. I suggested trying to equalize pressure yesterday but the problem is that there are 20 drain valves that feed directly into a common drain and they don't all drain simultaneously. I like the idea of stepping down the pressure between multiple valves but that would be a total redesign of the pipe plan we have. If that's the right thing to do though it's worth the expense.

Joe

 

[Danlap]

Joe,

Kindly not put my suggestion as it is. I am sure there were good feasibility reason why your system designed as current. And my point just from Ball valve and valves in general.
Not really sure about the end connection. I presume it is Raised face according to ASME, then you have the option of (similar face to face dimension) Ball, gate, globe, Plug.
From tightness point of view from better to worse are Plug, Globe, gate and Ball.
If you don't have flow restriction concern, then Plug or Globe might do the trick.
Gate if:
- installed (normally for dirty and fouling service advisable to install stem horizontal orientation) to mitigate pocketing in the cavity
- and maintained correctly (it will still 'pocket'ing some medium left over) by means of cleaning. This you can do by closing the fill valve (assuming it still tight), dismantle the drain valve, purge it with steam, etc. periodically
The approach might work also. Sufficient tightness for quite some time.

Your problem might be resolved with special valve such as Triple Offset Butterfly valve, Thru Conduite gate valve. Unfortunately they come in large sizes (2"/3" or above) and for some price.
Else, if I were you. Do some pilot with Ball valve with ceramic Seat as your suggestion. Inspect the sealing area afterwards (50 cycle??), it might be as simple as that. If it works, apply to others and stock the Ceramic seat or other suitable material in your warehouse. There is still a risk though about the Ball (as it is) vs the new stronger Seat, but you'll never know if not give it a try

Regards,
MR


All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected