Should the pneumatic or manual mode be selected for the daily operation of the pneumatic valve at the base of the spherical tank?
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Our spherical tank has two valves for inlet and outlet; the valve at the tank base is a pneumatic valve. This tank is used as a storage device for liquefied gas and for loading liquefied gas onto ships. I would like to ask whether it would be better to change this base valve to a pneumatic type to enable remote control via computer, or to keep it as a manual valve on-site in order to prevent the valve from closing automatically due to failures and thus avoiding pressure buildup in the system
Does your DCS have interlocking? If so, it needs to be set to automatic mode. You said there are two lines entering the tank – do both have pneumatic valves, or is only the inlet line equipped with a pneumatic valve? It is necessary to have a high liquid level interlock for shutdown, but we have not activated an interlock for low liquid level. It’s mainly to prevent the pump from running dry. However, all of this is contingent on the pneumatic valve and its interlock system still being functional.
It is a consideration from a safety perspective, providing a double safeguard; since there is already a manual valve in place, it facilitates emergency shutdown.
Setting it to automatic is good, as it allows remote control; manual control is only used in abnormal operating conditions, and it is switched to manual mode temporarily to ensure safety.
Agree with the person above. However, I’d like to share some experience: in our ball tank area, pneumatic valves were previously used at the root valve positions. But once the stem of one of those pneumatic valves broke and it stopped functioning, and it was not possible to remove it for repair. So now, during maintenance, we gradually replace the root valves with manual valves, using pneumatic valves as a secondary valve.
Both valves on our spherical tank are pneumatic valves. The interlock mechanism is set such that the pneumatic valve on the branch line operates; the pneumatic valve at the base of the tank on the main line remains in an open state. What’s unclear is whether this valve should remain in a manual or pneumatic mode when it’s in the open state. The main considerations are as follows: 1. If it’s in manual mode, it won’t be able to operate immediately in an emergency situation； 2. If it is pneumatic, a failure in the pneumatic system will cause the valve to close, resulting in pressure buildup in the device.
Generally, the pneumatic valve for tank roots and the interlock for high liquid level alarm in spherical tanks are valves that remain open to prevent excessive liquid from entering the spherical tanks
Since the pneumatic valve at the bottom of the tank on the bus needs to remain open, you should set it in the manual position. This is how we consider it.
It’s hard to answer. To be honest, we’ve tried having the pneumatic valve close automatically under normal conditions, but when it’s operated manually, it doesn’t function automatically – it’s really contradictory