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Pressure Seal Gate Valve

1. Product Overview

cast steel pressure seal gate valve

A pressure seal gate valve, cast steel, 900LB.

 

The pressure seal gate valves supplied by Metals Valve are mainly used in high temperature & high pressure applications such as power-plant steam service. The pressure sealed bonnet-body joint is a more positive way of sealing compared to its bolted bonnet counterparts because the internal pressure of the valve is used for bonnet sealing. As the line pressure is elevated, the load between the sealing surface of bonnet and tapered gasket tends to be increased – the higher the line pressure(valve internal pressure), the greater the sealing force against the bonnet gasket. Hence a more effective sealing can be achieved. Metals Valve’s pressure sealed gate valves are available in cast/forged carbon steel, alloy steel, or stainless steel materials furnished with end connections of butt welding(BW), socket welding(SW) and flanged(RF/RTJ). They are designed as per API 600 and ASME B16.34 covering pressure ratings of Class 600, Class 900, Class 1500, Class 2500. See more technical specifications of pressure sealed gate valves.

2. Design Features

Pressure Seal Design

cross view of gate valves' pressure seal bonnet design

Fig-1: The pressure-seal cross view of high pressure gate valve:segmented thrust ring, seal ring, and metallic gasket.

As illustrated in Fig-1, the pressure sealed bonnet-body joint of a high pressure gate valve is constructed by proper arrangement of body, bonnet, metallic gasket, seal ring, segmental thrust ring, retainer, body cover and a couple of bolts & nuts. The lower end of the bonnet is outwardly sloped to form a sealing contact with the inverted frusto-conical surface of the metallic gasket. The metallic gasket, usually made of soft steel material, is held down by a segmented thrust ring which is inserted into the annular groove of the valve body. The words “segmented” or “segmental” refer to the thrust ring consisting of a plurality of segments all of which may be cut from a single ring. A seal ring made of hard metal is placed between the thrust ring and the gasket and serves to distribute pressure on the thrust ring the gasket preventing deformation of the top surface of the relatively soft gasket. Both the metallic gasket and the seal ring shall be furnished with spaced threaded holes for ease of removing and maintenance. Besides, A – There shall be a 1° angle between mating surfaces of the bonnet slope and the gasket slope. This wedged design ensures a tight seal at either low or high line pressure. B – The interior sealing surface at the body neck shall be welded with a stainless steel inlay to provide finer grain and smooth finish as well as better corrosion resistance. C – Radial bores are furnished in the valve body through which a knock-out pin may be inserted for driving the segmental rings out of the groove. D – A small end bevel on the gasket to prevent it from scraping or catching in the groove.

Seating, Stem, OS&Y

Seating & Stem of Pressure Seal Gate ValveOutside Screw & Yoke(OSY) of PSB gate valve
The design features of pressure sealed gate valves:
(1) T-shaped blow-out proof design of the stem.
(2) Flexible wedge design to adapt to slightly misalignment caused by internal stress or deformation.
(3) Both the wedge and seat ring shall be hard-faced with ER410 or Stellite 6(Co-Cr A) overlay respectively.
(4) Outside Screw & Yoke, rising stem and non-rising handwheel.

3. Material Selection

C.S & S.S & Low Temp.

Part NameCarbon SteelLow Temp.Stainless Steel
HandwheelDuctile IronDuctile IronDuctile Iron
Stem NutASTM A439 D2ASTM A439 D2ASTM A439 D2
YokeASTM A216 WCBASTM A352 LCBASTM A351 CF8M
PackingGraphiteGraphiteGraphite
BodyASTM A216 WCBASTM A352 LCBASTM A351 CF8M
BonnetASTM A105ASTM A350 LF2ASTM A182 F316
WedgeASTM A216 WCB+ER410ASTM A352 LCB+ER410ASTM A351 CF8M+STL 6
Seat RingASTM A105+ STL 6ASTM A350 LF2+STL 6ASTM A182 F316+STL 6
StemASTM A182 F6aASTM A182 F6aASTM A182 F316
RetainerASTM A105ASMT A350 LF2ASTM A276 420
Body CoverASTM A216 WCBASTM A352 LCBASTM A351 CF8M
Segmental Thrust RingASTM A105ASTM A350 LF2ASTM A276 420
Bonnet Seal RingAISI 1045ASTM A276 420ASTM A276 420
Bonnet GasketASTM A182 F304ASTM A182 F304ASTM A182 F316L
Bonnet StudASTM A193 B7ASTM A320 L7MASTM A193 B8
Bonnet NutASTM A194 2HASTM A194 7MASTM A194 8
Yoke StudASTM A193 B7ASTM A320 L7MASTM A193 B8
Yoke NutASTM A194 2HASTM A194 7MASTM A194 8
EyeboltASTM A193 B7ASTM A320 L7MASTM A193 B8
Gland FlangeASTM A105ASTM A350 LF2ASTM A182 F316
GlandASTM A276 420ASTM A276 316ASTM A276 316
Gland NutASTM A194 2HASTM A194 7MASTM A194 8
BearingSS316 + PTFESS316 + PTFESS316 + PTFE
Name PlateSS304SS304SS304
RivetCopperCopperSS304
1. Conventional carbon steel, stainless steel, and low-temp materials for pressure seal gate valves.
2. Body materials listed in this table are cast steel. Forged steel body can be provided upon request.
3. Bonnet materials are furnished in forged steel to provide finer grain structure for a tight seal.
4. For sizes 4" and smaller, the bonnet gasket shall be made of graphite.

High Temperature Alloy Steel

Part Name1-1/4Cr-1/2Mo2-1/4Cr-1MoCr-Mo-V
HandwheelDuctile IronDuctile IronDuctile Iron
Stem NutASTM A439 D2ASTM A439 D2ASTM A439 D2
YokeASTM A216 WCBASTM A216 WCBASTM A216 WCB
PackingGraphiteGraphiteGraphite
BodyASTM A217 WC6ASTM A217 WC9ASTM A217 C12A
BonnetASTM A182 F11ASTM A182 F22ASTM A182 F91
WedgeASTM A217 WC6+ER410ASTM A217 WC9+ER410ASTM A217 C12A+ER410
Seat RingASTM A182 F11+STL6ASTM A182 F22+STL6ASTM A182 F91+STL6
StemASTM A182 F6aASTM A182 F6aASTM A182 F6a
RetainerAISI 4140AISI 4140AISI 4140
Segmental Thrust RingAISI 4140AISI 4140AISI 4140
Pressure RingAISI 4140AISI 4140AISI 4140
Bonnet GasketASTM A182 F304ASTM A182 F304ASTM A182 F304
Bonnet StudASTM A193 B16ASTM A193 B16ASTM A193 B16
Bonnet NutASTM A194 4ASTM A194 4ASTM A194 4
Yoke StudASTM A193 B16ASTM A193 B16ASTM A193 B16
Yoke NutASTM A194 4ASTM A194 4ASTM A194 4
EyeboltASTM A193 B16ASTM A193 B16ASTM A193 B16
Gland FlangeASTM A276 420ASTM A276 420ASTM A276 420
GlandASTM A276 420ASTM A276 420ASTM A276 420
Gland NutASTM A194 4ASTM A194 4ASTM A194 4
BearingSS316 + PTFESS316 + PTFESS316 + PTFE
Name PlateSS304SS304SS304
RivetSS304SS304SS304
Material selection for pressure seal gate valves:
1. C-Mo, Cr-Mo, Cr-Mo-V, Ni-Cr-Mo, & Cr-Fe high-temperature alloy steels:
    Cast: ASTM A217 WC1; WC6, WC9, WC11, C5, C12; C12A; WC4, WC5; CA15.
    Forged: ASTM A182 F1, F11, F22, F5, F9, F91.
2. Forged steel materials are preferable for body & bonnet due to the finer grain structure.
3. Other materials are available upon request.

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Wedge Gate Valve

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