Valve Actuators
Valve Actuators - This is ICEweb's Technical Information on Control and Quarter Turn Valve Actuators.
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Shutdown (SDV) and Blowdown (BDV) Valve Actuator Sizing and Torque Requirements
Correct specification of torque values for Blowdown and Shutdown Valves is absolutely critical to ensure integrity of a facility as the operation of these valves must meet the reliability and availability requirements. The following criteria give a guideline of the requirements, however it must be stressed that any design must meet the Safety and Integrity Level (SIL) defined for the facility. SDV and BDV valves also must be tested and verified in accordance with the facility Safety Case, Failure Modes and Criticality Analysis (FMECA) and Reliability Centred Maintenance (RCM) requirements.
Blowdown Valves (BDV) (Normally Open – Spring to Open) Actuator Torques
BDV Valve Start to Open Torque
Actuator Spring Start Torque - A safety factor of 100% (i.e. 2 times) should be applied on top of the valve start to open torque. This is defined as the torque at the 'compressed spring state' at the start of the emergency shutdown blowdown operation.
BDV Valve Reseat Torque (Valve Open Torque)
Actuator Spring End Torque - A safety factor of 25% (i.e. 1.25 times) should be applied on top of the valve opening torque. The spring should provide a torque of 1.25 times the valve open torque at its relaxed fully open emergency shutdown blowdown state.
BDV Valve Running Torque (Resistance Torque)
Actuator Spring Running Torque and Air Running Torque (Minimum Torque Produced by the Actuator) - A safety factor of 50% (i.e. 1.5 times) should be applied and maintained on top of the required valve running torque during the close and open valve running cycles.
BDV Valve Start to Close Torque
Actuator Air Start Torque - Pneumatic operator beginning torque should be 2 times the valve closing breakout torque at the start of the plant blowdown reset.
BDV Valve Reseat Torque (Closing Torque)
Actuator Air End Torque - Pneumatic operator end of stroke torque should be 1.25 times the valve closing torque. This is at the end of the closing stroke (The plant operating BDV Valve closed state).
Shutdown Valves (SDV) (Normally Closed– Spring to Close) Actuator Torques
SDV Valve Start to Close Torque
Actuator Spring Start Torque - A safety factor of 100% (i.e. 2 times) should be applied on top of the valve start to close torque. This is defined as the torque at the 'compressed spring state' at the start of the emergency shutdown operation.
SDV Valve Reseat Torque (Valve Closing Torque)
Actuator Spring End Torque - A safety factor of 25% (i.e. 1.25 times) should be applied on top of the valve closing torque. Hence the spring should provide a torque of 1.25 times the valve closing torque at its relaxed fully closed facility emergency shutdown state.
SDV Valve Running Torque (Resistance torque)
Actuator Spring Running Torque and Air Running Torque is the Minimum Torque produced by the Actuator during the closing or opening cycle. A safety factor of 50% (i.e. 1.5 times) should be applied and maintained on top of the required valve running torque during close and open running cycles.
SDV Valve Start to Open Torque (Valve Start to Open Torque)
Actuator Air Start Torque - Pneumatic operator Start to Open torque should be 2 times the valve opening breakout torque at the start of the facility shutdown reset.
SDV Valve Reseat Torque (Valve Opening Torque)
Actuator Air End Torque - Pneumatic operator end of stroke torque should be 1.25 times the valve opening torque at the end of the opening stroke (The facility operating SDV Valve open state.
Proper Actuator Design and Selection Reduces Down Time - Donald Weeks - Covers Valve and Actuator Technology, Torque and Actuator Sizing - from Flowserve
Trends in Pneumatic Spring Return Valve Actuator Selection - Ian M. Turner - When sizing pneumatic actuators for fail-safe valves, torque safety factors can vary depending on project specifi cations, and valve torques can vary from break to open, running and end to close positions. End-users normally determine the valve safety factor during the design stage and valve manufacturers, therefore, do not need to add extra contingencies. Essentially, these safety margins are determined with the goal that the valve should operate smoothly throughout its service life irrespective of the process condition. Increasingly, the safety factor applied when coupled with the specifi ed minimum sizing and normal supply pressure range for actuator selection, can result in selected actuator output torques exceeding the maximum acceptable stem torque (MAST) specifi ed by the valve manufacturer. In the oil and gas industry, for example, three different application categories for safety margin are commonly defined for on/off actuator valves - from Matic Actuators.
Torque Testing - This Covers: The Importance of Torque Testing and Actuator Selection, The Need for Torque Testing and The Use of Safety Factors When Specifying Actuators - from Geograph Energy.
Valve Shear Torque
Maximum Allowable Stem Torque (MAST) - Ball valves (rotary valves) are used as ESDVs/BDVs in critical services like shutdown, isolation and blow down application. Engineers endeavour to ensure reliability and integrity of actuator and its components. However as far as stem components are concerned sometimes either give little attention to mechanical integrity of stem or leave it to valve vendor and assume “Stem design is sufficient enough to withstand actuator torque”. Unfortunately this is always the case, Stems do fail!!! If stem key of an ESDV has failed OR damaged in open position……. What can happen …? It will not close when there is a close command and this may lead to disastrous situation - from Piping Engineering.
Valve Actuator Closed Loop Breathing
Closed Loop Breathing - This is a technique to ensure that corrosive or saline air cannot enter the internals of the valve on the breathing side of the valve. It is very popular in the Offshore Oil and Gas Industry and on Coastal Refineries etc - thanks to Rotork for this excellent schematic.