Pressure Seal Bonnet Gate Double Disc

ASME B16.34/API 600

Cast or carbon alloy steel, outside screw and yoke, rising stem, non-rising handwheel, welded-in seat rings, removable yoke sleeve, gland repacking under pressure.




Pressure seal valves are best fit for vertical stem / horizontal flow installation. Special cases can be evaluated and developed on request.



The spoked handwheel is fabricated from steel pipe. The hub is coupled to the yoke sleeve by means of a key. Larger valves are equipped with a bevel or spur gear gearbox unit.


They are in forged steel and are supplied in two pieces, self aligning design to allow the gland to slide parallel to the stem even if the eyebolts are unevenly tightened.


The forged steel gland bolts are of the eyebolt type which can be swung outward for ease of gland repacking. They are fixed to the bonnet by hinge pins.


It is machined in the same grade of the body or in superior alloys, if required. The pressure seal design keeps it tight to the body at high pressures even if bolts are loose or material dilatation occurs. It can be cast or machined from bar. It incorporates a stuffing box sized in accordance with the API standard, and in case can be extended for very high temperature applications. A locking flange with a set of bolts pulls the bonnet outward, against the gasket, giving a preload for initial sealing between body and bonnet.


It is basically supplied in graphite for best fit up to class 1500 and in AISI 316L stainless steel for 2500, carefully machined to provide a perfect tight seal. Upon request, AISI 316L can be installed on every pressure rating.


It is integral with the bonnet and hardfaced and will provide a perfect tight seal between stem and bonnet, which will allow emergency repacking operation even under pressure.


The stem is part of the trim and is available in a wide range of materials in accordance to API 600 or customer’s requirements. The stem is provided with a T-shaped head. A ground backseat is provided to ensure a perfectly tight seal to the stuffing box when the valve is fully open. The stem is highly finished in order to minimize friction and prevent damage to the packing. The thread is trapezoidal ACME type. All the stem sizes comply with the API 600 standard.


The body is in carbon or stainless steel and is available in many other CRA. It is carefully designed for total reliability, low pressure drop and simple maintenance. The basic dimension, i.e. wall thickness, face to face and flanges comply with the relevant API and ASME standards. Wall thickness and design can be both B16.34 or API600. The body neck is cylindrical in order to host the pressure seal bonnet. The body is basically supplied with renewable welded-in seats. Bosses are provided for drain taps or by-pass piping. The internal surfaces in contact with the fluid can be fully lined or cladded for improved corrosion or erosion resistance.


The rings are part of the trim of the valve. Welded-in seat rings are supplied as a standard. The two seating surfaces in the closed position provide a seal against pressure from both ends of the valve. They can be externally threaded and internally notched for easy installation and dismantling. Special attention is given to the seating surfaces which are ground and lapped for a tight seal.

The wedge effect between the two discs converts downward stem force into axial force and forces the parallel discs firmly against the valve seats, providing a seal against pressure at both ends of the valve. The central yoke ring forces one of the two discs during seating action and transmits the stem action to the disc assembly. It also keeps the discs aligned together during the travel.

Belleville springs packing ensures rapid unseating during opening operation.

Content 10

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