A U-tube arrangement for monitoring, observing, or measuring gas flow or gas generation of in a closed system can include a U-tube having a first arm, a second arm, and a bridge connecting the first arm to the second arm; a liquid disposed in the U-tube; an attachment conduit for coupling to the closed system and in fluid communication with the first arm of the U-tube and the closed system; a first valve for controlling fluid flow between the first arm of the U-tube and the closed system; an external conduit in fluid communication with the second arm of the U-tube and either an external atmosphere or external pressure source; and liquid level sensors disposed along at least one of the first arm or the second arm.

Provided are a device and a method for measuring fluid flow and pressure under a hyper-gravity environment. Two liquid reservoirs, a liquid level monitoring system, a flow monitoring system, a pumping system, and a pressure monitoring system are fixed to a base plate and disposed on a geotechnical centrifuge, where a flow pump is connected to an oil outlet of the geotechnical centrifuge; a pneumatic ball valve is provided with a gas source and connected to a gas outlet of the geotechnical centrifuge; and signals from the liquid level monitoring system, the flow monitoring system, the pumping system, and the pressure monitoring system are transmitted to a control center via a cable. The method includes: disposing the device on the geotechnical centrifuge, and acquiring fluid flow and pressure through the liquid level monitoring system and a pressure meter under a hyper-gravity environment.