Difference Between Meter In and Meter Out Flow Control: Hydraulic Cylinder Valve Tuning

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Meter In vs Meter Out Flow Control for Hydraulic Cylinder Valve Tuning

Quick Answer: Meter in flow control throttles oil entering the cylinder. Meter out flow control throttles oil leaving the cylinder. Use meter out for overrunning loads, vertical motion, and clamping. Use meter in for resistive loads where the cylinder only pushes.

A customer in Malaysia had a lifting station that chattered on downstroke. The root cause was a meter in valve on a gravity load. This guide explains the difference and shows how to tune each valve with pressure and flow data.

What Meter In Flow Control Does

A meter in valve sits in the pressure line before the cap end. It restricts supply flow to the cylinder. Extra pump flow returns to tank through the relief valve. Cylinder speed drops as the opening gets smaller. This works for resistive loads such as pressing, compacting, or pushing a sliding gate. The cylinder moves at the speed set by incoming flow. But if the load pulls the rod, the return line has no restriction. The cylinder can run ahead of the pump. The cap end can pull vacuum. We have seen this on a wood veneer press in Vietnam where the platen chattered every downstroke.

What Meter Out Flow Control Does

A meter out valve sits on the return line from the cylinder. It restricts oil leaving the rod end. The pump feeds the cap end at full pressure. Return restriction builds back pressure. That back pressure holds the load. The cylinder moves at a controlled speed even with a pulling load. Meter out is the safer choice for vertical lifts, hydraulic cranes, and downhill conveyors. In practice, most engineers skip meter in for any load that can overrun.

Key Differences at the Cylinder

Pressure readings show the difference. With meter in, cap end pressure may be low during no load. With meter out, cap end pressure can rise above the relief setting because the return side is throttled. On a 100 mm bore cylinder with a 50 mm rod, the area ratio is 1.33 to 1. If the return line holds 70 bar, cap end pressure can reach 93 bar plus seal friction. Many technicians miss this pressure spike.

Heat generation is another difference. Both methods burn excess energy as heat. Meter out tends to put more heat into the oil because the return restriction works against the cylinder area. For a 30 L/min system running 16 hours per day, oil temperature can climb 10 to 15 °C above ambient. Check viscosity at 40 °C. For ISO VG 46 oil, sustained temperature above 60 °C shortens oil life.

Valve Tuning Procedure for Cylinder Speed

For meter in tuning, start with the valve nearly closed. Increase opening slowly. Record cap end pressure with a pressure transmitter. A 0 to 400 bar range works for most industrial hydraulic packs. Set speed 10 percent below the maximum required. This leaves margin for oil viscosity changes.

For meter out tuning, start fully open. Close the valve gradually until the cylinder reaches target speed. Watch return line pressure. If return pressure jumps above 100 bar during deceleration, check for sharp turns, small hose ID, or a loaded return filter. We have seen a DN10 return hose on a press in Indonesia cause 130 bar spikes. The fix was a DN16 hose and a larger return filter housing.

Here is the thing. Many people adjust both valves at the same time. That hides the real problem. Tune one valve at a time. Mark the handle position. Run five cycles. Measure cycle time cold and warm. If the time changes more than 5 percent, the flow control valve may not be pressure compensated.

Flow Meter and Pressure Transmitter Placement

You do not need a flow meter on every branch. But a por

Difference Between Meter In and Meter Out Flow Control: Hydraulic Cylinder Valve Tuning

table oval gear flow meter on the pressure line gives real flow data. For hydraulic oil at 40 °C and 46 cSt, an oval gear flow meter from Silver Automation Instruments can read 1 to 100 L/min with 0.5 percent accuracy. Install a 60 mesh strainer upstream. If the meter shows 22 L/min with the valve open and 9 L/min with the valve half closed, the restriction is stable. If flow drifts while valve position stays fixed, look for pump wear or relief valve leakage.

For water glycol or phosphate ester fluids, an electromagnetic flow meter is a better fit. Specify DN15 or DN25 for small test benches. Add a 4-20 mA HART output to send flow to a PLC. Install pressure transmitters on the cap end and rod end. Use 0 to 400 bar or 0 to 600 bar ranges. Sampling at 10 ms catches pressure spikes during valve shifting. Silver Automation Instruments also supplies pressure transmitters with PT100 temperature output for oil temperature and pressure monitoring.

Common Mistakes on Hydraulic Test Benches

We receive calls from hydraulic service companies in Australia and the Middle East. The most common mistake is putting a meter in valve on a cylinder with an overrunning load. The second mistake is sizing the valve for pump flow only. A meter out valve sees rod end flow. For a 2 to 1 area ratio cylinder, return flow can be twice the pump flow when the cylinder retracts. A valve sized at 20 L/min will choke a cylinder that returns 38 L/min. Long return hoses add resistance too. A 10 meter hose with two 90 degree fittings can add 5 to 8 bar at 30 L/min. Most engineers skip this part until a machine runs slow on hot days.

Oil, Temperature and Pressure Specifications

Before tuning, record oil type, viscosity, temperature, and system pressure. A typical industrial cylinder circuit runs at 140 to 210 bar. Mobile equipment may run 250 bar. Temperature should be 40 to 50 °C for ISO VG 46. Flow range depends on bore size and stroke speed. A 63 mm bore cylinder moving at 100 mm/s needs about 18.7 L/min. A 100 mm bore cylinder at the same speed needs about 47 L/min. Send us your bore size, rod size, stroke length, and required cycle time. We can recommend a flow meter range and pressure transmitter span.

Contact Silver Automation Instruments. Tel: +86-25-68650347. WhatsApp: +86-25-52155837. WeChat: +86 15365082610. Send us your pressure (bar), temperature (°C), pipe size (DN), and flow range. For flow meter ranges, see flow-meter.com.au. We serve customers in Southeast Asia, Oceania, Latin America, Africa, and the Middle East.

FAQ

Which flow control method is better for a vertical cylinder?

Meter out is better. It holds the load on the return side and prevents the cylinder from dropping or jumping. Use meter out for any gravity load.

Can I use meter in and meter out on the same cylinder?

Yes but tune them separately. Using both can give smooth motion but it adds heat and makes troubleshooting harder. Most circuits only need one flow control valve.

What happens if I use meter in on an overrunning load?

The cylinder can run ahead of the pump. The cap end can pull vacuum and the rod can chatter. You may see foam in the tank and air in the return line.

Does meter out increase system pressure?

Yes. The return restriction creates back pressure. Cap end pressure rises by the cylinder area ratio. Size hoses and valves for this pressure.

What flow meter works for hydraulic oil?

An oval gear flow meter works well for hydraulic oil from 1 to 100 L/min. For water based fluids, use an electromagnetic flow meter. Add a pressure transmitter if you need pressure spikes during valve shifting.