Control Valves & Safety Valves
Control valves and safety relief valves are the two key valve families for process control and overpressure protection. A control valve takes a signal from the control system and continuously regulates flow, pressure, temperature or level by changing its opening; it is the final element of an automated control loop, and its flow characteristic, rangeability and leakage class directly determine control quality. Control valves are divided by design into single-seat (high sealing class, low leakage), cage-guided (stable guiding, multi-stage cage for cavitation and noise control), rotary eccentric (V-port, suited to solids-laden and viscous media) and pilot-operated pressure-reducing types (stable outlet pressure, high regulation accuracy). Leakage classes follow FCI 70-2 (Class I–VI); design and manufacture follow IEC 60534 and GB/T 17213. Safety valves balance media pressure against spring preload, opening automatically on overpressure and reseating as pressure falls; they are the final overpressure protection for pressure vessels and piping systems. Selection is based on set pressure and required discharge capacity, to ISO 4126 and API 520/526.
Spring-Loaded Safety Relief Valve
The Spring-Loaded Safety Relief Valve uses spring preload to balance the medium pressure. When the system pressure exceeds the set pressure, the disc is lifted and the medium is discharged to relieve the pressure; the valve recloses automatically once the pressure falls to the reseating pressure. It is the final overpressure protection device for pressure vessels and piping systems. Selection is based on set pressure and discharge capacity. Enclosed or open bonnets, metal or soft seats and a lifting lever for manual discharge and testing are available. The design follows ISO 4126 and API 520/526, and the valve is suitable for overpressure protection of steam, gas and liquid media.
Pilot-Operated Pressure-Reducing Valve
The Pilot-Operated Pressure-Reducing Valve consists of a main valve and a pilot valve. The pilot valve senses the outlet pressure and controls the opening and closing of the main valve, automatically reducing the high inlet pressure to the set outlet pressure and holding it stable. It offers high regulation accuracy, small outlet pressure fluctuation and high flow capacity, and maintains a stable output as flow varies. It is suitable for pressure reduction and stabilization in steam, compressed air, water and oil systems, and is widely used for pressure control in district heating, gas supply and industrial lines.
Rotary Eccentric Control Valve
The Rotary Eccentric Control Valve uses an eccentric rotary plug that both rotates and moves eccentrically, so the plug lifts clear of the seat during opening and closing without rubbing, combining the high capacity of a rotary valve with the shutoff performance of a control valve. The plug port is V-shaped and provides an approximately equal-percentage flow characteristic; its strong shearing action suits the control of fibrous, particulate and viscous media. The valve is suitable for pulp, wastewater and chemical slurry duties that are prone to clogging.
Cage-Guided Control Valve
The Cage-Guided Control Valve uses a cage design in which the plug is guided up and down inside the cage. The long guiding surface gives good stability and strong vibration resistance, and the cage windows can be configured to change the flow characteristic and the number of pressure-reduction stages. Multi-stage pressure-reduction cages effectively suppress cavitation and flashing and reduce noise, making the valve suitable for high differential pressure, cavitation-prone and noise-sensitive duties. The cage can be replaced as a complete unit to change the Cv value and flow characteristic, which simplifies maintenance; it is one of the most widely used control valve designs in the process industry.
Single-Seat Control Valve
The Single-Seat Control Valve uses a single-plug, single-seat design with only one sealing surface, giving low leakage and a high shutoff class. Combined with a pneumatic diaphragm actuator and a valve positioner, it continuously adjusts the valve opening in response to the control signal to achieve automatic control of flow, pressure, temperature or level. The plug is piston-shaped and offers equal-percentage or linear flow characteristics; the leakage class can reach FCI 70-2 Class IV/V. It is suitable for small and medium bore lines where regulation accuracy and tight shutoff are required and differential pressure is moderate.