These Sitecna LK04 lock-up valves were required for double acting actuated process control valves destined for Russia and had to be suitable for operating temperatures down to -40degC and complete with EAC CU TR 010 and 012 certification. These valves have options for EAC or ATEX certification and capable of operating temperatures down to -55degC.
The lock-up valve works by sensing the pressure at the signal port and balancing this against the adjustable spring. Once the signal pressure falls below the preset pressure, the valve closes both pairs of inlet and outlet ports to trap the compressed air within the valve actuator and prevent it from moving. This is a safety feature to prevent uncommanded valve operation in the event of falling supply pressure.