Cryogenic Gate Valves

The gate valve is characterised by the movement of the ‘wedge’ (obturator) being approximately parallel to the plane of the mating body seat.

Advantages
1. When the valve is fully open there is a clear unobstructed flow path along the pipeline, this gives better flow characteristics than globe valves. Typical resistance factors are between 0.3 and 1.0, the higher value being for reduced port valves.

Disadvantages
1. Due to the sliding action of the obturator over the machined body seat, wear of the seal and seat takes place especially if particulate contamination is present in the line, gate valves therefore have not been used in situations where tight shut off is critical over long service life.

2. The conventional gate valve has a metal seat machined into the body, when damage occurs the body requires removing from the line and in welded installations this can be a difficult and costly operation.

3. The conventional design of gate valve has a tapered wedge obturator with metal to metal or PTFE2 wedge seals; one of the major draw backs with this design being used at low temperatures is that differential thermal expansion will occur during warm up after the valve has been closed, this causes increased pressure on the wedge/body seat faces and in turn demands a high break out force on opening; actuated valves especially are prone to sticking with a resultant sudden “noisy” opening leading to damage of the valve and closely surrounding equipment.

Applications
Typical application being the trailer pump inlet valve (usually actuated for emergency shut off) where flow restriction would cause pump cavitation, also the delivery valves on trailers where unrestricted flow is required to reduce fill times.

The Bestobell gate valve has been designed to remove these drawbacks and give a full bore valve with a sealing mechanism that gives trouble free service and easy maintenance when required. This is achieved by providing a flexible obturator sealing disc to compensate for thermal expansion coupled with lapped seat faces to greatly reduce seal wear. In sizes that allow (DN50 and above), replaceable body seat rings are also fitted for ease of maintenance if line contamination causes damage to seats and seals.

The Bestobell gate valve has been tested on systems where water has been present and found to give superior service against globe valves, this is attributed to the vertical sliding action of the wedge coupled with the fact that if water does freeze in the stem/wedge assembly then the slight movement caused by this melting during warm up does not affect the sealing performance; consequently the valve has been used as the main fill valve on static storage tanks with excellent results.