ESD Fuel Gas Valves

[SILVIALE]

Hello,

I'm new on valves design.

I need to specify three ESD valve, to make a double block and vent configuration for a fuel gas line.

I’m not sure how to size the body and how to determine whether i should use a ball or a butterfly valve?

Is there a standard can guide me in the whole design process?

How do I get de deltaP i need to design? I’ve read son articles and says I should design based on the max pressure in the system as a deltaP, I’m not sure.

Please help,

Regards.

 

[pennpiper]

Point #1 - You are not "Designing" a Valve. You are only "Selecting" a valve that already exists. I am reasonably sure you already have these valve types in your system Specifications.

Point #2 - You only need to contact an Actuator Company and tell them what you are trying to do. They will be able to furnish an actuator and the linkage required to close the two Main Line valves and open the Vent valve.

Example:

http://www2.emersonprocess.com/en-us/brands/eim-actuators/pages/eimhome.aspx

http://bray.com/

https://www.google.com/search?q=Val...TxyYCICg&ved=0CIABELAE&biw=1024&bih=665&dpr=1

prognosis: Lead or Lag

 

[LittleInch]

Ok, you say you're new to this so let's just check a few things. You say ESD. The actual definition of this is not really fixed, but is described in company standards and project isolation philosophies.

What it means to most people is a fail safe valve which closes on loss of signal or power supply, i.e. it is held open, normally against a spring, but occasionally against a solenoid valve which has the line from an accumulator acting on a piston. Either way, this valve is a critical safety element with high requirements for reliability and normally not cheap. The system you describe sounds more like a process isolation system, as I have rarely seen a requirement for an auto DBB ESD System on a fuel gas supply.

If this is a ESD system I haven't seen many with a butterfly valve, but maybe that's just me.

There are a number of guides, but no real standard. You tend to find company standards or philosophies that describe the minimum requirements dormant on system, pressure and action.

Delta P for closure is the full DP the valve could ever see. As it closes, torque increases and DP can build up rapidly. Opening DP is up to you to determine, but most people go for full DP, even though opening like this would probably wreck the seats, sometimes you need to do it.

If you go for a low DP to open against, you need to find a way of easily equalising pressure across the valve and the cost saving often is quite low.

Sizing is a process design issue looking at flow and pressure. What you need to do us fill in a valve and actuator data sheet. Most valve vendors will supply you a blank or they're in the back of your valve spec.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

I prefer 1/4 turn to open ball valves. Butterfly valves are not considered positive shutoff in my book. Gates require too many turns for quick opening ESD service. Plugs may stick closed.

Independent events are seldomly independent.

 

[LittleInch]

Most ESD valves are normally open and then close in an emergency, but some Blowdown or venting valves can be held closed and then open to a flare, vent or drain.

I agree with BI, nearly all ESD valves I've seen are ball valves due to simple operation and high reliability.

One other aspect of an ESD system is that the valves should not normally be used for process control or shutdown, but be a completely independent, high integrity system.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

Good Point. Saudi Aramco, for example, as do many other industry safety leaders, specifically require a totally process-independent ESD system and ESD valves must be operated ONLY by THE universal, and, or, a locally initiated, ESD shutdown signal. This will often require that two valves be located immediately next to each other, one for process control, the other ESD only.

Independent events are seldomly independent.

 

[dcasto]

if you want to be cheap, the main block on the supply side should be a valve with a good seal, gate, HP ball whatever. The same for the vent, because you don't want a leak. The valve closest to the user of the fuel can be a cheap butterfly.

 

[BigInch]

Then it's only a single block and bleed, IMO.

Independent events are seldomly independent.