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『A Meter-out Flow Control Circuit: Pneumatic component velocity regulation standards.』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)
A Meter-out Flow Control Circuit: Pneumatic Component Velocity Regulation Standards
Quick Answer: A meter-out flow control circuit regulates cylinder speed by throttling the exhaust air, not the inlet air. This method produces smooth motion under changing loads and is the preferred speed control for most double acting pneumatic cylinders. Use ISO 6358 and ISO 8778 data when selecting speed control valves and flow meters.
What Is a Meter-out Flow Control Circuit?
A meter-out circuit places a flow control valve on the exhaust port of a pneumatic cylinder. The inlet side gets unrestricted air. The exhaust side gets a needle valve or throttle check valve. The piston speed depends on how fast air leaves the cylinder. When you close the needle valve, the exhaust flow drops. The piston moves slower. When you open it, the piston moves faster.
Most engineers choose meter-out for horizontal and vertical loads. The exhaust restriction creates a back pressure on the piston. This back pressure acts like a cushion. It absorbs load changes and reduces jerky motion. In a vertical cylinder application, the back pressure prevents the piston from dropping too fast when the load pulls downward.
Meter-out vs Meter-in: What Works in Practice
A meter-in circuit throttles the supply air. This setup is common for single acting cylinders and small spring return cylinders. However meter-in control can produce unstable motion. Because air is compressible, the pressure on the inlet side changes quickly and the cylinder may jump forward. In practice, meter-out control gives better repeatability for double acting cylinders.
We have seen this on customer sites many times. A paint manufacturer in Southeast Asia had a pneumatic mixer lift that moved unevenly. The original design used meter-in control on a 63 mm bore cylinder. The cylinder pushed a 40 kg load and the speed varied by plus or minus 20 percent. The customer moved the flow control valve to the exhaust side. The speed deviation dropped to under 5 percent without changing the cylinder size.
ISO 6358 and ISO 8778 for Pneumatic Velocity Control
ISO 6358 gives a method to measure the flow characteristics of pneumatic components. Two values matter for speed control sizing. The sonic conductance C value shows how much air can flow through the component at choked flow. The critical pressure ratio b value shows the pressure ratio when flow stops being choked. A speed control valve with a higher C value allows more exhaust flow for a given pressure drop. A lower b value keeps the flow stable over a wider range of downstream pressure.
ISO 8778 defines the standard reference atmosphere for pneumatic testing. The values are 20 degrees Celsius, 100 kPa absolute pressure, and 65 percent relative humidity. Most manufacturers report C and b values under these conditions. When you compare two pneumatic speed control valves from different suppliers, check that both use ISO 6358 data. Without this standard, the numbers are not comparable.
Sizing a Meter-out Speed Control Valve
Start with three numbers. You need the cylinder bore in millimetres, the stroke length in millimetres, and the desired travel time in seconds. Then calculate the average piston speed. For a 50 mm bore cylinder with a 200 mm stroke and a target time of 1.0 second to fully extend, the average speed is 0.2 metres per second. Next calculate the exhaust flow rate using the rod side area and the piston speed. This gives you the required volumetric flow in litres per minute at standard conditions.
Add a safety factor of 1.3 to 1.5. Air leaks, fitting re
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Pressure Monitoring and Flow Metering in Pneumatic Circuits
Air supply pressure affects exhaust flow and cylinder speed. A drop from 6 bar to 5 bar can reduce the speed by 10 to 15 percent in many pneumatic systems. This is why we recommend a pressure transmitter on the main air header. A Silver Instruments pressure transmitter with 4-20 mA HART output and a range of 0 to 10 bar can track supply pressure changes. When the pressure drops, the control system can alarm before speed variation becomes a production issue.
For compressed air flow measurement, a thermal mass flow meter works well. A Silver Instruments thermal mass flow meter with DN25 insertion probe and 4-20 mA output can monitor total air consumption at 0.6 MPa. On a food packaging line in Vietnam, the customer installed a DN25 thermal mass flow meter on the main air supply. The data showed that two high speed actuators consumed 45 percent of the total air volume. The plant then resized the speed control valves and reduced air waste by 18 percent.
FAQ: Meter-out Flow Control Circuits
Why is meter-out control better for pneumatic cylinders?
Meter-out control creates a back pressure on the exhaust side. This back pressure resists load changes and smooths the movement. It works well for horizontal and vertical cylinders. Meter-in control is common for single acting cylinders, but it can cause jumpy motion on double acting cylinders.
Which ISO standards apply to pneumatic speed control valves?
ISO 6358 defines the flow characteristic test method for pneumatic components. It reports sonic conductance C and critical pressure ratio b. ISO 8778 fixes the standard reference atmosphere for these tests. Always compare C and b values from the same standard.
When should I use meter-in instead of meter-out?
Use meter-in for single acting cylinders with spring return. Also use meter-in when the load pushes against the cylinder and you need controlled supply pressure. For most double acting cylinders, meter-out gives more stable speed.
What details do you need for a meter-out valve quote?
Give us the cylinder bore, stroke length, supply pressure in bar, load mass in kg, and the required travel time. We also need the thread size and the air fitting type. These numbers let us calculate the exhaust flow and select a suitable speed control valve.
Can Silver Instruments supply flow meters for pneumatic velocity regulation?
Yes. We supply thermal mass flow meters for compressed air, pressure transmitters for air headers, and electromagnetic flow meters for process fluid lines. For a pneumatic actuator control loop, we often recommend a pressure transmitter plus a thermal mass flow meter. Send us your air pressure in bar, pipe size in DN, and the number of actuators running in parallel.
Need a flow meter or pressure transmitter for your pneumatic velocity control loop? Contact Silver Automation Instruments. Tel: +86-25-68650347. Whatsapp: +86-25-52155837. WeChat: +86 15365082610. Tell us your pressure in bar, temperature in Celsius, pipe size in DN, and flow range. We will reply within one working day.