API · ASME · DIN · EN standard industrial valves
Parallel Slide Gate Valves
Parallel slide gate valves seal positionally: a spring presses two parallel closure members together for low-pressure seating, then rising line pressure pushes them against the seats so the seal tightens as the medium pressure grows — self-reinforcing sealing aimed at high-pressure, high-temperature service such as steam and feedwater lines. The range covers NPS 2" to 88" (DN50 to DN2200) at Class 300 to 4500 (PN25 to PN760), with carbon steel, alloy steel and duplex stainless steel bodies, RF, BW or RTJ end connections, and manual, pneumatic, electric or hydraulic operation. The design buys three specific advantages: parallel discs sliding on flat seats cannot be thermally bound the way a wedge is clamped after a hot shutdown, so high-temperature steam lines with frequent thermal cycles use this type precisely to remove that failure mode; operating torque stays low with no wedging to seize, easing actuator sizing; and at high class the pressure-seal bonnet reinforces seat sealing the same way line pressure does - sealing force grows with differential pressure, while disc springs or internal spreaders set the practical low-differential sealing limit. It is strictly an on-off isolator: holding it partially open erodes the flat seats and drives high-frequency disc chatter, so a separate regulating valve is required for flow control, and trapped solids or piping-distorted seats hold the discs off their faces - flush the line before final closure and keep piping alignment true. Maintenance is workshop-friendly: disassemble without special tooling, replace disc springs, lap or refurbish seat faces, keep gland compression right, grease stem threads, and exercise the valve periodically so deposits cannot build up on seats that normally stand open or closed. Choose rising stem where vertical clearance allows position indication to matter, non-rising stem for confined or underground installations. Tightness is proven per API 598 (shell, closure, backseat) with ISO 5208 / EN 12266-1 as the European frame; API 600 governs bolted-bonnet process-isolation valves while API 6D adds pipeline-specific duties including fire testing, sour service, cycling, and automatic body-cavity pressure relief that the API 600 frame does not require. Selection turns on the class against steam conditions, the body alloy against the medium, and the end connection against the piping spec.
Part of the Gate Valves family
Last updated: 2026-11
Family specifications
| size range | NPS 2"~88"(DN50~DN2200) |
|---|---|
| pressure class | Class 300~4500（PN25~PN760） |
| pressure class | 300~4500（PN25~PN760） |
| body materials | Carbon steel, Alloy steel, Duplex stainless steel |
| end connections | RF, BW, RTJ |
| operation | Manual, Pneumatic, Electric, Hydraulic |
| applications | High pressure and high temperature services such as steam and feedwater |
| selection thermal binding elimination vs wedge | Parallel slide gate valves avoid thermal binding because the two discs slide parallel to flat seats instead of being forced between inclined seats, so body contraction during shutdown cannot wedge the closure member tight. This makes the design the usual choice for high-temperature steam lines that undergo frequent thermal cycles. |
| selection pressure assisted sealing low deltap basis | Sealing force comes from line pressure acting on the downstream disc, so seat tightness improves as differential pressure rises. At low pressure the disc springs or internal spreaders alone provide the baseline seat contact, which sets the practical low-differential-pressure sealing limit of the design. |
| selection no wedging seizure and torque | Because the discs do not wedge, opening and closing torque stays low and there is no wedging action to seize the valve after thermal expansion. This reduces actuator sizing and lowers seat wear over repeated operating cycles. |
| selection pressure seal bonnet self energizing | For high-pressure classes the bonnet is typically of pressure-seal type: internal pressure forces the gasket more tightly into its seat, so bonnet sealing improves as pressure rises. This matches the self-reinforcing behavior of the parallel-disc seat seal. |
| selection hp steam water isolation positioning | The parallel slide gate valve is an established valve type for high-pressure steam and high-pressure water isolation duty, offered in ratings from ANSI 150 to ANSI 1500 with tight shut-off obtained from line pressure rather than mechanical wedging. |
| selection catalog size class envelope example | A typical commercial parallel slide gate valve envelope runs from small sizes up to DN900, in ANSI class 150 to 600 with flanged or butt-welded ends. Wider class ranges are offered by power-plant specialists, so class availability must be confirmed per manufacturer. |
| failure throttling chatter seat erosion | Parallel slide gate valves are on-off isolation devices only. Holding the valve partially open for throttling produces turbulence across the nearly closed flat seats, eroding the seat faces and driving high-frequency disc chatter, so a separate regulating valve is required where flow control is needed. |
| failure trapped solids seat leakage | The flat, closely finished parallel seats are vulnerable to debris: suspended solids trapped between the faces hold the discs off the seat and cause leakage, and piping loads that distort the seats have the same effect. Line flushing before final closure and correct piping alignment are the preventive measures. |
| failure thermal binding wedge mechanism contrast | Thermal binding, the classic wedge-gate failure after a hot shutdown, occurs when the cooling body contracts and clamps the wedge between the seats, seizing the valve or buckling the stem. The parallel-disc design is selected precisely to remove this failure mode from high-temperature service. |
| installation routine maintenance and exercise | Routine care consists of checking gland packing compression, lubricating the stem threads, and periodically cycling (exercising) the valve so deposits cannot build up on the seats and disc edges - an important regime for valves that normally stand open or closed for long periods. |
| installation seat refurbishment workshop tooling | The valve can be disassembled for inspection without special equipment: seat faces can be examined, internal disc springs replaced, and sealing surfaces restored with standard workshop tooling, which keeps lapping or seat refurbishment practical in normal maintenance. |
| installation stem choice vs vertical clearance | Rising-stem versions give clear visual open/closed position indication but need vertical space above the valve; non-rising-stem versions keep the stem height fixed and suit confined installations such as underground vaults and cramped pipe racks, at the cost of less obvious position indication. |
| standards api598 closure testing reference | Seat (closure) tightness for steel gate valves of this family is generally proven per API 598 as referenced by the valve specification, with shell, closure and, where fitted, backseat tests. ISO 5208 / EN 12266-1 rate classes are the equivalent European acceptance frame. |
| standards api600 vs api6d scope | API 600 governs bolted-bonnet steel gate valves for refinery and process isolation, while API 6D is the pipeline-valve standard covering gate valves for transportation systems and adds pipeline-specific requirements such as fire testing, sour service and operational cycling. Project specifications may require one or both. |
| standards api6d cavity pressure relief | Where a gate valve is built to API 6D for pipeline service, the body cavity must be able to relieve trapped overpressure automatically in addition to the normal shell and seat tests - a requirement not present in basic API 600 process-isolation valves. |
| peer size range severe service psg | 4 – 36" |
| peer pressure class severe service psg | ASME / ANSI Class 150 – 4500 |
| peer body materials severe service psg | Carbon steel (A216 WCB) – standard Alloy steel (A217 WC9, A217 C12A) – standard Stainless steel (A351 CF8M) – standard |
| peer compliance nuclear silver psg | ASME B16.34 PED Nuclear ASME III Class 1, 2 and 3 Nuclear Safety Related – 10CFR50 Appendix B SIL |
| peer end connection default psg | Buttweld – standard Other end connections available upon request |
| psg bidirectional zero leakage shutoff | Bi-directional, zero-leakage shutoff |
| psg disc seat carbide overlay | The valve discs and seats have been overlaid with the same carbide overlay (68-70 RC) |
| psg seat lapping vacuum tight | and are lapped to achieve a bubble-tight seal under all pressure conditions, including vacuum. |
| psg web guide parallel discs | The web guide (which is also carbide overlayed) ensures the discs are kept parallel, whether the valve is in the open or closed position. |
| psg wear honing not galling | As the valve is cycled under differential pressure, the extremely hard surfaces continually hone and polish each other instead of scratching and galling. |
| psg pressure seal bonnet graphite composite | The pressure seal bonnet has been designed with a graphite composite seal. |
| psg bonnet bolting cold preload | The bonnet has sufficient mechanical bolting to ensure the seal does not relax during periods when the system is not pressurized. |
| psg stem gland hardfaced polished | The stem and gland are hardfaced and polished. |
| psg backseat chrome carbide | The back seat is coated with chrome carbide (typical hardness 68-70 RC) and polished to achieve a bubble tight seal. |
| peer size range double disc psg | NPS 2 1/2 to 24 DN 65 to 600 |
| peer pressure class double disc psg | 150 to 1500 PN 25 to 260 |
| peer seating material double disc psg | Seating Material: Metal |
| double disc design service envelope | this exclusive disk and wedge design resists effects of extreme temperatures, gross thermal transients, high and low differential pressures, and dual-phase fluids. |
| double disc bonnet internal access | Increased plant and personnel safety is made possible by bonnet design, allowing easy access to valve internals while minimizing radiation exposure |
| peer standards nuclear double disc psg | ASME B16.34 ASME Section III |
| peer actuation configs double disc psg | Motor Actuated Motor Operator Hydraulic Actuated Hydraulic Operator |
| psg disc cooldown no stress | There is no mechanical stress exerted between the discs or problems associated with the cooldown of the fluid. |
| sealing principle | Positional seal, Line pressure as sealing force |
| special features | Spring between the two closure members provides an initial seal during low pressure conditions, Higher medium pressure creates the primary seal, the higher the medium pressure the better the sealing performance |
Scope & source notes
| type level parameters | A Chinese vendor page under the same English name lists Flexible/Solid Wedge materials and 1.0-2.5 MPa water/sewage duty, while OEM references position the parallel slide type as high-pressure steam/water isolation up to ANSI 1500 - the vendor page appears to describe a low-pressure slide-gate family; its parameters are product-specific, not type-level. |
|---|---|
| sealing direction framing differs by construction | Sealing-direction framing differs by construction: one source characterizes API 600 gate valves as unidirectional sealing relying on bolted-bonnet pre-load, while parallel-slide references describe line-pressure-assisted bidirectional sealing - the framings reflect different gate constructions under the standards, not one sealing rule. |
| temperature range | Temperature envelope differs materially between catalog sources (-196 to 593 C on one catalog versus -29 to 425 C on another); the tenant entry quotes no single type-level envelope and per-material limits must be confirmed per manufacturer. |
Ordering & documentation
Documents
Ask for the documentation set with the inquiry — typical items (material certificates, test reports to the listed inspection standard, dimensional drawings) are confirmed and supplied with the quotation.
Quotation
Send the medium, temperature, pressure, size and connection for a quotation-ready inquiry. Lead time, MOQ and price are confirmed at quotation, together with the documents to be supplied with the order.
Sample & supply
Supply terms, order quantities and lead time are agreed per order — state the destination country and required schedule with the inquiry.
Storage & shipping
Store valves with seats and seals protected from UV, ozone and deformation, and keep end-face protectors on until installation; storage limits and shipping arrangements for the selected materials are confirmed at quotation.
Frequently asked questions
What sizes and pressure ratings are available for parallel slide gate valves?
The published size range is NPS 2"~88"(DN50~DN2200), and the published pressure ratings are Class 300~4500（PN25~PN760）. Availability of a specific size and rating is confirmed at quotation.
What materials are parallel slide gate valves available in?
The published specification lists body materials: Carbon steel, Alloy steel, Duplex stainless steel. Material availability for a specific size and rating is confirmed at quotation.
What end connections do parallel slide gate valves support?
The published specification lists RF, BW, RTJ as the available end connections. The connection for a specific size is confirmed at quotation.
What should a quotation inquiry for parallel slide gate valves include?
The governing standard and class, nominal size, body and seat materials, the service medium with temperature, and the destination — anything missing is confirmed during quotation.
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