Should such operating conditions be handled with pressure or flow switches?
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This is a process condition with very low flow rate; I would like to consult experts in control and automation. The process conditions are as follows: Medium: Alcohol with a concentration of over 95%. Flow rate: 5 L/h. Process description: A core filter is connected to the outlet at the bottom of a small alcohol storage tank (500 L); the pressure drop across this filter is 0.2 bar. The fluid then passes through a small pump, whose inlet is located below the inlet of the alcohol storage tank, and the outlet of this pump is connected to a small nozzle. Question: Due to the low flow rate and the small size of the pump, I need to install something between the filter outlet and the small pump so that it can detect when the filter is clogged and there is no flow, or when the flow rate is less than 2 liters, and then send an alarm signal to shut off the pump’s power supply.
Normally, a differential pressure switch is used in such situations
A differential pressure controller should be installed, with the pressure measurement points located before and after the filter. Regarding the set value: You can measure the pressures before and after the differential filter when the flow rate is 2 L, and then determine the appropriate set value for the differential pressure controller.
It seems that your operation is manually controlled; if that’s the case, install a differential pressure gauge with on-site indication to measure the pressure before and after the filter. When the pressure difference increases to a certain value, it indicates that the filter is clogged. It’s economical and practical this way. As for the reason for low flow rate: 1. The filter is clogged, resulting in low flow; this can be seen from the differential pressure gauge ； 2. In actual operating conditions, if the flow rate is low, increase it.
A differential pressure switch is the same as what is known as a differential pressure controller. The price ranges from 100 to 1000, depending on the operating conditions
I’m very grateful for everyone’s help; I’ve also considered using a differential pressure gauge. But the flow rate is too low, and the pressure difference is also small. Does anyone know of manufacturers that produce such low values? Please give some recommendations. Also, the control is done by an automatic controller. Explosion protection is also required.
In such cases, you need an explosion-proof differential pressure switch; it’s not difficult to find one. Since the medium is a liquid, there is also a differential pressure related to flow rate, but such switches aren’t cheap. In fact, a flow controller can also be used for monitoring – you determine an appropriate flow range, and if the flow rate is outside that range, it means there’s a blockage.
I think a flow switch is better, as it’s more accurate