Design Previous common practice has been to use two valves (Fig 1), such as plug or ball valve designs, in series with a bleed facility located between them in order to establish the sealing integrity of the upstream valve. This configuration is far from optimum as more space is required, with considerable extra weight quite apart from the additional maintenance requirements of having two valves and the extra associated costs.

The Solent & Pratt Double Block and Bleed design (Fig 3) utilizes our well established, patented triple offset segment valve (TOSV). Two seals are incorporated on the disc segment thus providing sequential sealing. The downstream seat is not spring loaded, as is the practice for trunnion mounted pipeline valves (Fig 2), which are also very heavy and expensive. Sealing integrity is therefore maintained should the upstream seat fail. When the valve is closed a channel between the two seats connects with a purge or bleed port in the valve body which is connected to an external outlet where an isolation valve or relief valve may be fitted for manual or automatic bleed. This compact Double Block and Bleed Design negates the need for using two valves in series.

Patented two direction valve geometry

The Solent & Pratt Triple Offset Segment Valve utilizes the well established patented valve geometry where the shaft is offset from the body in two directions (1) and (2), whilst the disc is a segment taken from a cone where the apex is offset from the center line of the valve (3). The disc (segment) of the valve houses a field replaceable metal laminate seal whilst the field replaceable seat ring is housed in the body of the valve.

Due to the valve geometry there is no interference or rubbing between seat and seal as the valve strokes through it’s full 90°.