Bypass or Hand jack

[thalathb]

Gents,

I know the system criticality plays a big roll here to design the valve with Bypass or Hand jack. But, does any one have tips or criteria to help for designing the Valves with bypass or Hand jack?

Thanks and Regards
TH

 

[thalathb]

does any one have tips or criteria to help for designing the Valves with bypass or Hand jack rather than criticality?

 

[JLSeagull]

Besides corporate standards, several factors can affect the decision to provide a control valve with a bypass or handwheel.

Onshore plants are less concerned about weight than offshore. Offshore may use few bypass valves; many bypass valves are used in similar onshore applications.

Lacking blocks and bypass you cannot service the control valve. If critical for operation you need the ability to service the control valve. Sometimes, parallel control valves with block valves are used in lieu of a bypass.

Modular packages permit taking a portion of the process down and operate at reduced rates. This permits servicing a control valve with neither a bypass or handwheel.

 

[unclesyd]

Are you talking about putting a hand wheel on bypass valve with an operator to use if the operator fails?

Some of our high pressure motorized steam bypass valves have hand wheels on the valves operator in case of valve operator failure. I can only recall one time that a bypass valve was operated with the hand wheel. It didn't take the mechanics too long to replace the faulty operator as they had to help operate the 24" valve using the hand wheel.

 

[KenA]

thalathb,
Another factor is size of control valve. As the control valve size increases, so does the size of the manual bypass valve and the size of the manual isolation valves around the control valve set. Larger size means more space required and more cost so larger sizes start to cause layout and financial worries. For onshore installations, design contractors tend to have size limits of between 8" and 12" where they deem a bypass valve to be impractical.

 

[thalathb]

Thanks all for your inputs.