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『Flow Meter with Auto Shut Off Automation: Linking Flow Relay Thresholds to Solenoid Safety Valves』Related information(v cone flow meter|rotary gas meter|gallon meter|gear meter|metal tube rotameter|glass tube rotameter|nutating disk meter|transit time ultrasonic flow meter|wedge flow meter|pd meters|hydraulic flow meter|ultrasonic water flow meter|water flow meter|air flow meter|magnetic water flow meter|oxygen flow meter|gas flow meter|argon flow meter|air velocity meter|gasoline flow meter|fuel flow meter|ultrasonic water meter|digital water meter|nitrogen flow meter|solid flow meter|Oxygen tank flow meter|digital water flow meter|diesel fuel flow meter|steam flow meter|02 flow meter|compressed air flow meter|oil flow meter|liquid flow meter)
Flow Meter with Auto Shut Off Automation: Linking Flow Relay Thresholds to Solenoid Safety Valves
Quick Answer: A flow meter with relay outputs can close or open a solenoid safety valve when flow crosses a set threshold. Set the relay threshold 10 to 20 percent below normal minimum flow for low flow trips. Wire the relay contact in series with the solenoid coil. Silver Instruments supplies electromagnetic, Coriolis, vortex, oval gear and thermal mass flow meters with relay outputs for this task.
Why Local Relay Trip Is Faster Than a PLC
Many sites read a 4-20 mA flow signal into a PLC and then command a solenoid. That path works but it has extra delay. The PLC scan time, network latency and output card response can add 2 to 5 seconds. A flow meter with an onboard relay can react in 0.2 to 1 second. That speed matters on a solvent transfer line running at 20 m3/h.
Most engineers skip this part. The flow meter relay should be a hard wired backup to the PLC. It should not be the only safety device. Use both layers when the fluid is flammable or corrosive.
Flow Relay Threshold Settings for Liquids and Gas
Start with the normal operating range of the process. Set the low flow trip 10 to 20 percent below the minimum stable flow. Set the high flow trip 10 percent above the maximum safe flow. For a DN50 line moving 18 m3/h, the low trip could be 14 m3/h and the high trip 22 m3/h.
Hysteresis matters. A 5 percent hysteresis works for many liquid batching lines. For compressed air or gas, use 10 percent. Gas flow can pulse after a compressor unloads. Without hysteresis, the relay will chatter and the solenoid valve will cycle too often.
Because flow can dip during pump start, use a 5 to 10 second bypass timer. Most batch controllers and flow meters with relay outputs include this timer. Without it, the low flow relay can trip every time the pump ramps up.
How to Wire a Flow Meter Relay to a Solenoid Safety Valve
Most Silver Instruments relay outputs are volt free contacts rated at 250 V AC, 3 A. Use the normally open contact in series with the solenoid coil for a close on low flow trip. When flow drops below the threshold, the relay opens and the solenoid closes. Use the normally closed contact if the valve must open on high flow.
Keep relay cables away from VFD output cables. Use shielded cable for relay runs over 10 m. Earth the shield at the panel end only. In ATEX Zone 1 or Zone 2 areas, wire the relay through a galvanic isolator or use an Ex d enclosure.
Recommended Silver Instruments Flow Meters with Relay Output
The SIL-EM electromagnetic flow meter covers DN15 to DN200. It has a pressure rating up to PN40, temperature up to 120 °C, and accuracy of 0.5 percent. It has pulse, 4-20 mA HART and two relay outputs. A water treatment contractor in Vietnam uses this meter to stop a dosing pump at 2 m3/h low flow.
The SIL-CMF Coriolis mass flow meter covers DN3 to DN150. It measures mass flow in kg/h, density and temperature. It has two configurable relay outputs. A che
The SIL-VF vortex flow meter handles steam, compressed air and natural gas from DN15 to DN300. It works at pressures up to 40 bar and temperatures up to 350 °C. The relay output can close a gas solenoid valve on low flow to protect burners.
The SIL-OG oval gear flow meter fits diesel, fuel oil and varnish. It covers viscosities from 1 to 1000 cP. It sends a pulse or relay trip when flow stops. Marine and power generation sites use it for engine fuel line shutoff.
The SIL-TMF thermal mass flow meter reads direct gas mass flow in kg/h or Nm3/h. It is common for purge gas and blanketing. The relay threshold can close a solenoid valve if purge flow falls below a safe level.
Installation Checks Before Startup
Confirm the upstream and downstream straight pipe lengths for the selected flow meter. For an electromagnetic meter on a DN80 line, use at least 5 DN upstream and 2 DN downstream. For a vortex meter, follow the straight run listed in the manual. Flow profile errors can shift the trip point.
Test the relay threshold with a signal source before process startup. Many sites run wet tests with water first. Check the relay action with a multimeter. Confirm the solenoid valve moves within the expected time. Record the trip point and the valve closing time in the site calibration log.
FAQ: Flow Meter Auto Shut Off and Solenoid Safety Valves
Can any flow meter drive a solenoid safety valve?
No. The meter must have a relay output or a batch controller with relay output. A 4-20 mA only meter cannot drive a valve directly.
What relay threshold should I set for low flow pump protection?
Set the trip 10 to 20 percent below minimum normal flow. For a pump minimum stable flow of 5 m3/h, set the relay to 4.2 m3/h with 3 percent hysteresis.
Does the relay output need an external power supply?
The relay contact is often volt free. You supply the solenoid coil voltage separately. Use 24 V DC or 230 V AC based on the solenoid valve rating.
Can the flow meter relay work in a hazardous area?
Yes if the meter has ATEX or IECEx certification. Route the relay wiring through a galvanic isolator or Ex d enclosure.
Which flow meter type is best for fast auto shut off?
A Coriolis or electromagnetic meter with local relay output is usually fast enough for liquid lines. For gas, a vortex or thermal mass meter works well. In practice, the solenoid valve closing time is often the limiting factor.
To specify a flow meter with auto shut off, send your pipe size (DN), flow range (m3/h or kg/h), pressure (bar), temperature (°C), fluid name and viscosity (cP). The Silver Instruments team will select a model with the correct relay output and setpoint. Contact Tel: +86-25-68650347, Whatsapp: +86-25-52155837, WeChat: +86 15365082610. Product data is available at flow-meter.com.au.