『Hydac Flow Meter: Sizing Electronic Volumetric Sensors for Fluid Power Hydraulic Power Units Skids』Related information(flow rotameter|digital flow meter|balo meter|hydraulic flow meter|volumetric meter|positive displacement meter|pitot tube flow meter|displacement meter|cfm meter|variable area flow meter|inline flow meter|differential pressure flow meter|calibrated flow meter|velocity meter|paddle wheel flow meter|oval gear flow meter|anemometer hvac|multiphase flow meter|doppler flow meter|thorpe tube flowmeter|heat flow meter)
Hydac Flow Meter Sizing for Electronic Volumetric Sensors on Hydraulic Power Unit Skids
Quick Answer: To size a Hydac flow meter or an equivalent electronic volumetric sensor for a hydraulic power unit skid, start with the actual oil flow range in litres per minute, oil viscosity in centistokes, and maximum working pressure. Most skid builders choose a positive displacement oval gear meter with a 4-20 mA output and a pressure rating above 250 bar. Silver Instruments supplies direct replacement flow meters for many Hydac volumetric sensor models with DN10 to DN50 connections.
Why Hydraulic Power Unit Skids Need Volumetric Flow Measurement
Hydraulic power units move oil through pumps, valves, filters, and heat exchangers. Flow rate tells you if the pump is healthy, if a filter is clogged, or if an internal leak is growing. Most system builders do not use magnetic or Coriolis meters here. They use positive displacement volumetric sensors because hydraulic oil can be 32 cSt to 68 cSt and the flow range is often 5 to 120 L/min.
Sizing Parameters That Decide the Meter Model
Send us these values before you pick a flow meter. The oil flow range is the biggest factor. A 100 L/min pump may only return 70 L/min through the return line. Do not size the meter at the pump nameplate unless the meter sits directly in the pump outlet. Most hydraulic skid meters go in the return line or a dedicated measurement branch.
Viscosity matters. Hydraulic oil at 40°C often ranges from 32 cSt to 68 cSt. At startup the oil can be 200 cSt or higher. An oval gear meter handles this easily. A turbine meter may not. Pressure drop must stay below 0.5 bar across the meter. Too much drop adds heat and cuts system efficiency.
Connection size is another factor. Common skid pipe sizes are DN10, DN15, DN20, DN25, and DN40. The meter must match the pipe or use adapters. Silver Instruments offers oval gear flow meters with BSPP or SAE threads for hydraulic manifolds.
Hydac Flow Meter Cross Reference and Replacement Options
Hydac offers electronic volumetric sensors for mobile and industrial hydraulic systems. Common models work with 10 to 100 L/min flow ranges and provide analog or switching outputs. Many Hydac flow meters use a gear measurement principle. This is the same principle used in Silver Instruments oval gear flow meters.
One difference is price and lead time. A hydraulic OEM in Vietnam replaced a Hydac flow sensor on a 300 L/min skid with a Silver Instruments DN25 oval gear meter. The meter used a 4-20 mA output and a 350 bar pressure rating. The replacement took 3 days to deliver from our Singapore stock. Field calibration matched the original sensor within 0.3 percent.
Output Signal Selection for PLC Control
Hydraulic power unit skids almost always use 4-20 mA signals. The signal goes into the Siemens or Allen Bradley PLC. Some users also need a pulse output for total volume or a HART signal for remote diagnostics. Silver Instruments supplies 4-20 mA, pulse, and HART versions of the same meter body.
Do not select a display only meter if the skid PLC needs a signal. You lose the main control loop. If you need local display plus signal, choose a meter with a small LCD and a separate 4-20 mA terminal.
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A customer in Malaysia ran a 200 litre tank with a 75 L/min pressure compensated pump. The return line flow was 55 L/min at 46 cSt oil viscosity. Operating pressure was 25 bar. Our recommendation was a DN20 oval gear flow meter with a range of 10 to 120 L/min, a 4-20 mA output, and a 350 bar safety rating. The meter had two switch outputs for high and low flow alarms. The total pressure drop at 55 L/min was 0.35 bar.
This installation took one technician half a day. The meter mounted directly into the return line with two BSPP fittings. No straight pipe run was needed because the oval gear principle does not need the same upstream calming length as a vortex meter.
Installation Pitfalls We See on Hydraulic Skids
In practice, most hydraulic skid builders ignore startup viscosity. One common mistake is installing a flow meter directly at the pump outlet without considering pressure pulsation. The gear meter can handle it but the signal may flicker. Use a small dampening loop or a meter with a built in flow conditioner. Another mistake is ignoring the return line temperature. Hydraulic return oil can run at 70°C or higher. Make sure the meter seals and electronics are rated for that.
We have seen a food processing plant in Indonesia specify a plastic body flow meter for a hydraulic return line. The oil temperature reached 85°C and the body cracked. Use stainless steel or aluminum bodies for hydraulic oil. Silver Instruments volumetric meters use aluminum or 316 stainless steel bodies with FKM or PTFE seals.
FAQ for Hydac Flow Meter Sizing on Hydraulic Power Units
Can Silver Instruments replace a Hydac flow meter on my skid? Yes. Many Hydac electronic volumetric sensors can be replaced with Silver Instruments oval gear meters if you match the flow range, connection size, and output signal. Send us the model code and we will confirm the cross reference.
What flow range do I need for a hydraulic power unit skid? Measure the return line flow at normal working temperature. A 75 L/min pump often returns 50 to 60 L/min. A DN20 oval gear meter covers 10 to 120 L/min and works for many skids.
Which flow meter works best for hydraulic oil with viscosity up to 100 cSt? Oval gear and gear flow meters work best. They hold accuracy from 5 cSt to 500 cSt. Avoid vortex and turbine meters for high viscosity or low flow hydraulic circuits.
Do you supply flow meters with 4-20 mA output for PLC? Yes. All Silver Instruments oval gear flow meters can be ordered with 4-20 mA, pulse, or HART output. You can also add a local LCD display.
What pressure rating is available for hydraulic flow meters? Standard aluminum bodies cover up to 400 bar. Stainless steel bodies cover up to 630 bar. Most hydraulic skid applications operate below 250 bar, so the standard rating is enough.
Send us your flow range in L/min, oil viscosity in cSt, pressure in bar, pipe size in DN, and the current Hydac model if you have one. We will reply within 24 hours with a replacement quote. Reach Silver Instruments at Tel +86-135-1213-1526, WhatsApp 86-135-12131526, WeChat +86 13512131526, or visit flow-meter.com.au.
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