A slam shut valve is typically only used in gas service, and it typically only has two criteria for actuation: overpressure and under-pressure. It typically requires manual reset by a human operator after actuation. With respect to actuation, a number of them are integrally actuated or self actuated. Both Fisher and Emerson have good articles on the topic.
An ESDV might indeed take the form of a slam shut if the service is gas and the only criteria for actuation are overpressure and under-pressure. Apart from that, an ESDV is typically a different style of valve with slower closure speed that can be used in liquid or gas service. Actuation of an ESDV is typically controlled by a signal from SCADA or a PLC, and the criteria for actuation can be a host of things other than pressure.
SNORGY,
I think your last point is the key difference--an ESD is part of a site-wide emergency scheme with any number of monitored parameters and criteria while a slam valve is locally controlled based on a very limited number of parameters (usually one and not part of the SCADA system).
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
IMO there is no real difference other than the speed of the actuator. A fast closing actuator could be nitrogen gas pressure holding the valve open against a spring supplying an immediate closing force when gas pressure is vented by a manual ESD switch, or remote SCADA signal. Slower closing speeds can be obtained with adjustable motor operators. ESD valves can have motor operators. Either a manual switch, vent valve, signal from a control room, or remote SCADA signal could trigger either form of operation. ESD means "Emergency Shut Down" and the designation is independent of valve type or actuator. ESD is only describing the function that the valve performs. The same type of valve or actuator could be used in non-emergency valve as well.
If it ain't broke, don't fix it. If it's not safe ... make it that way.
I agree that they could be the same valve and actuator technology, but when I hear "slam valve" I'm looking for something without wires going to it that is process-related, not safety related (different spares strategy, different testing frequency, etc). If it is tied into site automation then an ESD is part of the site ESD strategy and subject to safety PM frequencies.
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The "slam shut" terminology should be "downgraded" in favor of stipulating the desired actuator type and required speed of closure. Then it could be hooked up to whatever system might be available to control it, or not, as the case may be.
If it ain't broke, don't fix it. If it's not safe ... make it that way.
So to sum up:
ESDV: site wide philosophy, safety related, no need to be fast actuating, linked to SCADA and/or Fire and gas/emergency shut down philosophy
Slam shut valve: local impact, process related, fast actuating, no link with SCADA or any PLC (I think there is always an uninterruptible power supply on a solenoid valve to shut the SSV in case of loss of control of the process)
But 2 related questions come to my mind:
1) Is there some regulations dealing with this difference (if possible if you know European regulations, I would take any regulations dealing with this topic though)?
2) Is there a regulation or best practice document dealing with the architecture of an ESDV (by-pass allowed with or without an ESDV on the by-pass, process use of the ESDV allowed if different PLCs are used with a priority for the Safety PLC...)?
Don't think I agree with "no need to be fast actuating". Sometimes you limit the speed of travel of an ESD if you are concerned about water hammer or other system shocks, but other times you want it to shut as quickly as physically possible.
I don't think "fast acting" is appropriate for the slam valve either. The issue is mostly "is it part of the safety strategy or part of the process strategy?" not how fast does it operate.
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
Bypass without its own ESD, if normally closed, would be OK, as for a black start valve to take fuel from upstream around the mainline ESD, that would be used to bring up the emegency generator, open ESD valves and then to restore normal operations.
UPS on a electric solinoid valve would be better used in the reverse position, where loss of power would open the solinoid valve to vent power gas which was holding the ESD open against a spring, rather than the UPS running a motor that closed a valve. Bad idea.
If it ain't broke, don't fix it. If it's not safe ... make it that way.
The UPS I was talking about is to keep passing the solenoid valve to keep the main valve open thanks to the pneumatic pressure of the gas inside the pipe. The loss of the UPS closes the main valve via the spring of the actuator.
The few times I've put in a process shut down that wasn't part of an ESD, I used pneumatics from the local process (not the site instrument air or control gas) and pneumatic pilots. When the condition I was concerned about happened the pilot dumped pressure to the slam valve and springs shut it. If I have to bring in power or control gas then the valve and its control are going to be more sophisticated than a "slam valve" (may still just shut, but it will have criteria, ranges, permissives, etc.) instead of "touch the setpoint and slam shut, manually open".
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
Slam shut to me just means the main valve is spring actuated, no matter what the speed might be in reality, as it's likely to be a couple of orders magnitude faster than a motor op.
If it ain't broke, don't fix it. If it's not safe ... make it that way.
To me the difference is that an ESD may still close softly while a slam valve just slams closed. For marine operations on liquid terminals, bu rule the ESD needs to actuate in 30 seconds regardless of size.
