Hello

I am currently specifying instrumentation powered electrically to achieve the following:

On the occurrence of a low pressure downstream of a PCV, a low pressure switch/transmitter will de-energize two upstream pumps via their individual on-off hand station.
From this same low pressure signal source we require the actuation of a shut-down valve to its Fail Close state.

The power supply will be sourced from nearby MCC and there is no instrument air on site.

To date I am looking at the PressureGuard self-contained hydraulic emergency shutdown system from Emerson, but this device will only bring forth the closure of th SDV. however I still need to de-energize the two high pressure pumps upstream.

Any recommendations would be appreciated.

 

Can you bring the contact of the PIT to the safety relay of the pumps in your MCC directly and let the MCC to kill the pumps. (I hope you MCC could take this signal)

 

The Pressure Guard self-contained hydraulic emergency shutdown system is very nice but I don't think you need it. Use a electric actuator for the SDV as well as for the PCV and you will be able to activate and control both from a hardware PIC situated in your MCC. The same contact from the PIC that you use to close the SDV with, can also be used, via some relays, to shut down the pumps upstream.

If you have to use the Pressure Guard it can still be done. but then you have to use the Pressure Matic Pilot that comes with the system in order to read the line pressure downstream separately from the pressure transmitter that is connected to your PIC in the MCC. Now to make sure it will work when you want it to work, you need to set the pressure trip point on the Pilot. that will give an hydraulic output to the Pressure guard, slightly higher than the trip point for the PCV. and then just install a solenoid valve in the hydraulic line between the pilot and the pressure guard. This will have the effect that if a pressure downstream goes low, the pressure pilot will activate first, but no action will take place since the solenoid valve in line to the pressure guard have to be activated as well via the PIC in the MCC which also control the action of the PCV and the two upstream pumps.

Like I said it can be done but my suggestion is that if you have not installed or bought anything yet, rather go for the electric actuator setup since these actuators can be setup as shutdown and control actuators. and you can also have both function for one actuator as well in that it will do normal modulating control until a 24V is removed. in which case it will be driven to its fail safe position.

The draw back is that should your main supply in the local MCC fail, your whole system fails. while if you use the pressure guard you can make the solenoid in the hydraulic line to open during a power failure and the system will at least go to the fail safe position on the SDV.

Something else on that is that you can get a build-in hydraulic back for the electric valves as well that will give you the assurance that the valve will go to the fail safe position during a main power failure. so they can be pretty safe and reliable as well. Problem is these kind of actuators are pretty expensive.

 

Hello

thank you for all of the feeback.

The recommendation to bring the contact of the PIT to the safety relay of the pumps in the MCC to kill the pumps will be implemented.

Secondly, the recommendation to avoid using the Pressure Guard self-contained hydraulic emergency shutdown system was taken to heart and an alternative elector-hydraulic actuator control system is now under consideration. Model EH-44, Manufacturer ATI.

http://www.atiactuators.com/assets/files/ATI_EH-44_ele-hyd-con-sys.pdf

Again I welcome further feedback towards the resolution of this installation

Regards

 

Hello,

In addition to my earlier response, I am looking at the WIKA Pressure gauge model 212.20.100 with model 821 switch contact to initiate the de-energizing of the circuit (ie the closure of the SDV and the de-energizing of the pumps)

http://www.wika.com.ar/upload/DS_AC0801_GB_793.pdf

Are there any thoughts/suggestions on the feasibility of using this Manufacture / model to activating the Low Pressure Switching functionality? A better manufacturer/model recommendation would be greatly appreciated

Regards

 

Electromechanical pressure switches need no power to operate, the line pressure on the sensor element activates the snap action electrical switch(es). Large elastomer diaphragms or bellows for lower pressures, metallic diaphragms or pistons for higher pressures. United Electric, SOR, Ashcroft.

United Electric has electromechanicals and an electronic model, the One Series, whose set and reset points are set with a pushbutton keypad, a huge time savings save compared to the time consuming, iterative 'setpoint calibration' needed to set or check electromechanicals, even if they have a graduated scale adjustment. The 8W models have 2 independent switch outputs. 4-20mA available for a continous output. Good switch if electrical power is available.

 

Thanks a lot for the feedback.

 

Why not use that PCV's controller contacts to do the shut down of the SDV and pumps instead of installing a separate pressure switch? Your PCV is controlled by something, a PLC or hardware PID controller that must have a input from a PT on the line somewhere. This controller will then control the PCV according to a setpoint set on this PID controller. Based on the input of the PT you should be able to set a couple of relay contacts on the controller or outputs from a PLC to activate at certain pressures so these contact can be used to stop your pumps and close your SDV. This is pretty much the standard way a control system like this will work.

Here is something you can look at w.r.t hydraulic backup electric actuators. They are the top of the range but very expensive.

http://www.rotork.com/en/product/index/skilmatic

 

Ashcroft offers the N-Series which is also sensor-based, with independent set & dead band, optional digital display, and 4-20mA output.

http://www.ashcroft.com/products/pressure_switches/N-Series-Nema-4-Electronic-Pressure-Switches.cfm