OEM Cast Steel Gate Valve Manufacturer & Factory

Bolted Bonnet (BB) designs utilize standard stud bolts and gaskets (spiral wound graphite with stainless inner/outer rings). While economical and straightforward to assemble, for ASME Class 900 and above, bolted bonnets require massive flange diameters and extremely high bolt-torquing to maintain gasket seating under pressure surges. A Pressure Seal Bonnet (PSB) reverses this geometry: internal pipeline pressure drives the bonnet upward against a wedge-shaped metallic or graphite gasket retained by a segmented thrust ring. Consequently, higher operating pressure results in a tighter seal, reducing valve weight by up to 40% and preventing thermal relaxation leaks in high-temperature steam lines.

We achieve zero-leakage / low-emission performance through three critical engineering controls: First, valve stems undergo precision centerless cylindrical grinding followed by roller burnishing, guaranteeing surface roughness of Ra ≤ 0.2 to 0.4 µm and straightness within 0.05 mm to prevent packing shearing. Second, our stuffing boxes utilize die-formed flexible graphite rings with braided carbon fiber anti-extrusion end rings. Third, we configure live-loaded disc Belleville springs on the gland studs to maintain constant compressive stress on the packing stack throughout hundreds of thermal expansion and contraction cycles.

For standard hydrocarbon applications, API Trim 8 (F6a / 13Cr stem with hardfaced seats) is common. However, for sour service meeting NACE MR0175 / ISO 15156, we specify API Trim 12 (316 stainless steel with Stellite Gr. 6 weld overlay) or Trim 5 (Full Stellite Gr. 6). Crucially, the stem material must undergo controlled tempering to ensure a maximum hardness of 22 HRC, preventing sulfide stress corrosion cracking. All base casting heats (such as ASTM A216 WCB or A352 LCC) also adhere to strict maximum carbon equivalent (CE ≤ 0.43%) limits and post-weld heat treatment (PWHT).

No. Gate valves are strictly designed for fully open or fully closed on/off isolation service. When cracked open in an intermediate throttling position, high-velocity fluid flow generates turbulent vortex shedding behind the unsupported wedge disc. This results in severe chattering, severe cavitation erosion across the narrow bottom clearance, and wire-drawing of both the seat ring and wedge face, destroying the valve’s ability to achieve bubble-tight shutoff. For throttling duties, globe valves or customized eccentric control butterfly valves must be specified.

All ZFA Valve production valves undergo 100% hydrostatic shell testing at 1.5 times the cold working pressure (CWP), high-pressure hydrostatic seat closure testing at 1.1 times CWP, and low-pressure pneumatic seat testing at 80 psi (6 bar) per API 598 or ISO 5208. For critical petrochemical and power contracts, we provide supplementary non-destructive examinations: 100% dye penetrant (PT) of hardfaced seating surfaces, magnetic particle testing (MT) of body/bonnet casting radii, radiographic testing (RT) or phased-array ultrasonic testing (PAUT) of critical sections per ASME B16.34 Appendix-I, along with full EN 10204 3.1 chemical and mechanical inspection certificates.

Standard carbon steel WCB gate valves (sizes 2" through 12", Class 150/300) are maintained in semi-machined component inventories, allowing complete assembly, testing, paint coating, and shipment within 15 to 20 calendar days. Large-bore models (14" to 48") or high-alloy grades (WC6, WC9, C12A, CF8M, Duplex) requiring custom pattern pouring, specific radiographic qualification, and specialized actuator mounting (ISO 5211 pads with spur or bevel gearing) generally require 35 to 55 working days from final approved engineering drawing sign-off.