B
Problem Statement: Erratic Flow Control In Auto or Manual Control
A transfer line exists between two pressurized tanks and tanks are the same size and are at the same elevation. A simple single loop flow controller sits on the transfer line to move a water based fluid from one tank at a higher pressure to the other. The flow meter is a T-series Micromotion and the valve is a Samson sanitary angle globe. Flow setpoint is 100 Liters/Hour. The valve is in a very controllable range of approx. 45%.
Flow control is excellent until the upstream tank is topped off, which then results in a higher static pressure plus overlay pressure relative to the valve inlet pressure. Both tanks are at the same elevation, thus the need for the overlay on the upstream tank to transfer to the receiving tank. When upstream tank is 1/4 full the flow control is good, but once the upstream tank is topped off, then flow control becomes erratic even with the flow controller in manual mode.
There is a local PI at the flow meter and control valve inlet and the pressure does not change coincident with the erratic change in flow. The downstream tank vessel pressure is rock solid and so what is causing the flow to be erratic? The only process difference is the increased upstream static pressure with a full tank. Filling the upstream tank changes the valve dp from approx. 8 psid to 12 psid. Fluid temp is a constant 25 degc.
Any helpful hints would be appreciated.
A transfer line exists between two pressurized tanks and tanks are the same size and are at the same elevation. A simple single loop flow controller sits on the transfer line to move a water based fluid from one tank at a higher pressure to the other. The flow meter is a T-series Micromotion and the valve is a Samson sanitary angle globe. Flow setpoint is 100 Liters/Hour. The valve is in a very controllable range of approx. 45%.
Flow control is excellent until the upstream tank is topped off, which then results in a higher static pressure plus overlay pressure relative to the valve inlet pressure. Both tanks are at the same elevation, thus the need for the overlay on the upstream tank to transfer to the receiving tank. When upstream tank is 1/4 full the flow control is good, but once the upstream tank is topped off, then flow control becomes erratic even with the flow controller in manual mode.
There is a local PI at the flow meter and control valve inlet and the pressure does not change coincident with the erratic change in flow. The downstream tank vessel pressure is rock solid and so what is causing the flow to be erratic? The only process difference is the increased upstream static pressure with a full tank. Filling the upstream tank changes the valve dp from approx. 8 psid to 12 psid. Fluid temp is a constant 25 degc.
Any helpful hints would be appreciated.