Gate Valve with Seat Flush 1

[Danlap]

Dear Valve professionals,

Requires some insights Re: Seat Flush on Gate valve.
Background: One of my Plant has some Fouling issues regarding PolyCycle Aromats (or PAK) in the past; Current Gate Valves were modified by adding Seat Flush connection in 2005, hence no fouling was ever reported again and result tight shut off.

Situations:
My company adding a new Plant (exactly similar services), however with an additional Discharge system (negative pressure instead of Positive pressure in order to make Seat Flush functions properly).
My old timer Operation still believe that Seat Flush (even though non-standard design) are still required for this application

Technical specification:
1. Gate valve (Wedge) already bought are Body: ASTM A105 ; Trim: AISI 410 + Stellite, and it will be mounted Horizontally
2. Due to spatial constraint, only Gate and Butterfly valve that meet the face to face dimension criteria
3. It is 8"-300# and 10"-300#, which most of Butterfly Valves manufacturer offers a Lugged type and non-fire proof BV. By this reason I put aside the BV option.

Question:
1. How does this Seat flush eliminates "potential pockets collecting unwanted debris" especially for sticky tracing as PAK.
2. How does it flush with Negative Pressure? This is a double Block (two Gate Valves) and Bleed system. Should I make additional modification? Change one of the valve? Change the material? etc.
3. Does this Seat flush modification will make the warrant (from the manufacturer) void?

Thank you beforehand for the constructive inputs,
Regards,
MR

Greenfield and Brownfield have one thing in common; Valve(s) is deemed to "run to fail" earlier shall compared to other equipments

 

[gerhardl]

Hello Muktiadi:

In my opinion you should evaluate your situation as follows:

1. Any fluid with tendency to stick will stick under most circumstances. If sticking previously it will most likely also stick now.

Conclusion: flushing to be provided. (Exception if pipeline and valves to be kept permanently under 'unsticking conditions'. This will not occur if normal atmospheric conditions give sticking, as you will have process stops for maintenance)

2. Sticking will be worst at corners and pockets, both when the gate is in closed position, and at upper construction (spindel, inner top and gate) when closing. There is a large number of valve constructions, details and qualities. Some are for many sticking fluids almost self- cleaning, others seems to be constructed to gather as much rest-fluids and particles as possible. You do not state if your valves are different or equal in inner construction compared to the old. The flushing does not eliminate pockets, it cleans existing pockets. Horisontal mounting (if allowed by supplier at all !) will only move sticking problems around a bit, and might give worse conditions for the valve operation in general.

Conclusion: Get the best possible construction, but add flushing anyway.

3. Vacuum: Regard vacuum compared to your other pressures (including surrounding) as a 'normal' pressure difference, only 'further down' the measurement scale. If this is a moderate vacuum (probably is) it should not be necessary to modify anything. (High or very high vacuum migt require checking that all sealings inside or for flanges for the valve is ok for this)

4. Modifying the valves:
Any modification not done at the valve factory or given OK by the manufacturor will break the warranty. The producer should however be interested in helping you solve the problem as this will both increase the market, experience and references if all goes well.

Conclusion: Discuss and agree with valve supplier.

Good luck!

 

[Danlap]

Hello gerhardl,

Thank you very much. Really appreciate your systematic inputs.
Indeed some cross-discipline issues (Operation, Valve design and material) are best elaborated by experienced person like you.

Since my (internal) client will order a standard (equal construction with previous valve) Wedge Gate valve. I would say, it is susceptible to (sticky) pocketing, thus I will endorse the additional modification of Flushing.
And ensure that extra mitigation / alarm / maintenance strategy to be added for preventing the valve leaking through the negative pressure side.
Better save then sorry.
Discuss and agree with valve supplier is an easy ones. The challenge is changing the mindset of my (internal) End user.

Regards,
MR



Greenfield and Brownfield have one thing in common; Valve(s) is deemed to "run to fail" earlier shall compared to other equipments

 

[gerhardl]

Thank you Muktadi!

( I had to smile at your 'challenge' - indeed a well known challenge almost everywhere!)