Balanced-bellows PRV

This is a PRV designed to minimize the effect of back pressure on its performance characteristics. 

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Figure 2 A typical balanced-bellows PRV. [Courtesy of Tyco Valves and Controls LP]...

Besides reduce the backpressure influence on PRV s disk, bellows has another usage. It sometimes is used to isolate the guide, spring, and bonnet fiom the relieving fluid. It is important that balanced-bellows PRV s bonnet be vented to atmosphere, since it is part of valve s design basis. 

Kd equals 0.74 for PRV sizing, if manufacturer s Kd is not avmlable, Kd equals 0.62 for rupture disk sizing. Kw equals 1.0 for conventional, pilot PRV, and rupture disk sizing. For balanced-bellows PRV, use Figure 9 to estimate its value. 

Balanced-bellows PRVs are spring-loaded valves with a bellows or some other means of balancing the valve disk to minimize the effect of back pressme. Typical valve configurations are shown in Figure 4.3 and Figure 4.4. 

Balanced-bellows PRVs are not normally used if a conventional PRV is acceptable. However, some operating companies prefer to install balanced-bellows PRVs for all scenarios simply because of possible change in future service conditions. 

Balanced-bellows PRVs can be used for higher back pressme up to 50% back pressure without reducing the back-pressure correction factor (for a 21% overpressure situation). 

Balanced-bellows PRVs are normally used when the back pressure exceeds 10%. 

Balanced-bellows PRVs are widely used for flashing service. 

If there is a choice between conventional and balanced-bellows PRVs, the conventional PRVs are a better option. 

The flow contingency shall be the maximum contingency flow through the valve. This is the maximum capacity of the relief valve. For convenhonal and balanced-bellows PRVs, the nonrecoverable pressure drop shall not exceed 3% of the PRV set pressure. 

Balanced-bellows PRVs for subcritical flow are designed using Equation 4.44. The back-pressure correction factor is obtained from tiie manufacturer. 

Conventional PRV is not suitable Recalculate using Balanced Bellow PRV... 

This program has been developed for conventional and balanced-bellows PRVs. However, this program can be used for pilot-operated PRVs, too. For pilot-operated PRVs, use ... 

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