RBV or MOV?

[ali.abbas]

Which of the following option is better for emergency isolation on natural gas lines,

• 1- RBVs with pneumatic actuators
  2- Motor Operated Valves (MOVs)?

[AbsarShah]

What do you mean by RBV?

[ali.abbas]

RBV is a Remote Block Valve. Its basically an isolation valve or ESD valve.
Question: Is there any standard that determines pneumatically operated valves or motor operated valves for purposes of isolation of a natural gas line during a fire?

[AbsarShah]

Okay, well, yes volume isolation needs to be enforced for pipeline applications.

MOV's MAY be used for shutdown applications, there is a variety of SIL-3 certified EH valves available on the market with spring return (enabling fail-safe position). You just have to take notice of your process requirements. Most significantly, the closure time. Especially with liquids, closure time is very sensitive. You need quick closure, but you don't need slam-shut, otherwise a surge can occur.

Then, since this is going to be a remote location, you need to consider the supply of power to the MOV - check with your electrical disciplines whether you can take LV cables to the distance that you require. Additionally, you will need a 415V UPS, since MOVs on emergency service will most definitely need to be powered from a UPS - a regular power supply will not do. So you can compare the cost of installing a 415V UPS, the feasibility of running power cables to remote areas against the option of pneumatic valves.

The point is, you can use a suitable MOV for isolation, but conventional pneumatic valves are more reliable. And in most cases, pneumatic valves will also prove to be more economically and technically feasible. Once you do a background study on all the requirements of both cases, you'll get a clearer picture of your particular scenario.

[ali.abbas]

Thanks Absar.
The central idea im taking here is that there is nothing against standards in using either an MOV or conventional pneumatic valves. It basically comes down to technical and economic feasibility.

What does the acronym "EH" refer to though?

[AbsarShah]

Electro-hydraulic. Because you will definitely not be using conventional electrical-only motorized valves for safety applications.

And yeah, there is nothing in the standards against using EH valves, because SIL-3 certified valve actuators are available on the market. But application of those is rarely every feasible, so a background study is a must here.

[ali.abbas]

Actually I was talking about using a conventional "Electrical-Only Motorized" valve here.

Whats wrong with using it for safety applications though?