Double Block and Bleed ball valve have evolved to replace the process of bolting together individual valves to provide dual isolation.

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Elinor White
5 years ago
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1 Bleed valve

2 Double Block and Bleed ball valve have evolved to replace the process of bolting together individual valves to provide dual isolation. This new assembly provides great savings in weight, space and installation times especially in instrument or instrument cage isolation. These savings can be as much as 60% in weight and studies have shown that a 70% installation time saving is also possible. However the greatest savings are to be seen in the reduction of leak paths to atmosphere, therefore reducing the risk of the potential hazards this entails. Dual isolation is a necessary requirement when maintenance is taking place down stream of the first isolation valve. Cavity venting is provided by either a ball or needle vent valve so that trapped pressure between the two isolation valves is safely vented.

3 The primary function of a double block and bleed system is for isolation and the secondary function is for intervention. Under certain conditions double block and bleed systems are needed to prevent product contamination or where it is necessary to remove essential equipment from service for cleaning or repairs while the unit continues in operation. Of course, such equipment must be provided with a spare or it must be possible to bypass it temporarily without shutting down the unit. The nature of the fluid, its pressure and temperature, and many other factors must be considered when determining the need for double block and bleed systems.

4 Generally, block Valves should be considered for the on-stream isolation of equipment if the fluid is flammable or otherwise hazardous, or if the fluid is in high-pressure or hightemperature service. Where double block Valves are used, a NPS ¾ or larger bleed Valve should be installed between the block Valves. The purpose of the bleed Valve is twofold. First, the bleed ensures that the upstream Valve is in fact tight before slipping in a blind off the downstream block Valve. The bleed connection also permits the safe withdrawal of moderate leakage from the upstream Valve to again assure the tight shutoff of the downstream Valve. Depending on the service conditions, it may be possible to use a single block Valve with a body bleed to provide double block and bleed provisions for on-stream isolation of equipment. Some Ball Valves, when equipped with a Valve body bleed between the seats, can also be satisfactory substitutes for double block Valves. Testing for double block and bleed quality Valves requires the pressure-testing of each seat, with leakage measured through the Valve body bleed as a means of substantiating the independent leak tightness of both the upstream and downstream seats of the Valve.

5 The Double Block and Bleed Ball Valve can perform the tasks of 3 separate Valves (2 separate isolations and 1 drain Valve) which apart from being hugely space saving can also save on weight and time due to installation and maintenance practices requiring much less work and the operator being able to locate and operate all 3 Valves in one location. Double block and bleed ball Valve operate on the principle that isolation can be achieved from both the upstream and downstream process flow / pressures This is achieved by two balls, valves are placed back to back, with a third "isolatable" Valve in the centre cavity. Once isolation has been achieved in one or more of the main process isolation Valves, the cavity that is created between these isolations can be drained. This is useful for flow diverting, sampling or injection situations, and for maintenance and or integrity check situations where seat leakage can be monitored through the third "bleed" Valve.

9 Double block & bleed ball valve DBB valve with locking device

10 Double block & bleed ball valve DBB valve with pneumatic actuator

11 Double block & bleed ball valve DBB valve with needle type bleed valve

12 Double block & bleed ball valve High pressure DBB valve Cryogenic type DBB valve with pressure relief valve

13 Safe Operation HermetiX Zero leakage stem packing Hermetix

14 Hermetix fire safe stem sealing design

15 Hermetix fire safe stem sealing design

steel material The thrust washer at the bottom of HermetiX stem seal & the

16 Hermetix fire safe stem sealing design Wear protection Thrust washer NOTE: Metal support (bearing) is made of impregnated sintered PTFE stainless steel material The thrust washer at the bottom of HermetiX stem seal & the wear protection washer on top of the HermetiX steam seal are made of PEEK VI

17 Double block & bleed ball valve 4 x 1 DBB valve with ANSI flange connection

18 Double block & bleed ball valve

19 Double block & bleed ball valve

20 Double block & bleed ball valve

21 Double block & bleed ball valve

DURASEAL. High Integrity, Double Block and Bleed Plug Valve.

DURASEAL. High Integrity, Double Block and Bleed Plug Valve. DURASEAL High Integrity, Double Block and Bleed Plug Valve www.franklinvalve.com How the DuraSeal Works An improved valve with a proven history We took an alternative path. Unlike many valve manufacturers