Orifice Plates
OB / OS / OM Series — Brass, Stainless Steel & Monel
RCM Industries orifice plates measure flow rate, reduce pressure, or restrict flow across a wide range of industrial applications. Available in three materials — Model OB (brass), Model OS (316 stainless steel), and Model OM (Monel) — these plates handle liquids, gases, corrosive fluids, and high-temperature service. Our flow nozzle design features a convergent, curved inlet profile with no discontinuities leading to a cylindrical throat section, delivering an excellent flow profile and low friction — especially suited for abrasive fluids that would erode traditional sharp-edge orifice plates.
Standard Features
- Three material options: Brass (OB), 316 SS (OS), Monel (OM)
- Flow nozzle design — curved convergent inlet, no sharp-edge erosion
- Pipe sizes ½″ through 3″ — three flow ranges per size
- Suitable for liquids, gases, corrosive and high-temperature service
- Flange-mounted wafer style — installs between standard flanges
- Differential pressure output: 207.6 in H₂O (brass) / 276.8 in H₂O (SS/Monel)
- Beta ratios from 0.22 to 0.65 for accurate DP measurement
- Weights from 2 to 6 lbs depending on pipe size
Typical Applications
Water Treatment
Process water flow measurement and chemical dosing verification
Chemical Processing
Corrosive fluid metering with SS or Monel construction
HVAC
Chilled and hot water loop balancing and flow verification
Oil & Gas
Fuel gas, natural gas, and hydrocarbon liquid measurement
Power Generation
Steam flow measurement and condensate return monitoring
Marine / Offshore
Seawater and brine service with Monel construction
Compressed Air
Plant air flow restriction and measurement
Pharmaceutical
Purified water and process fluid metering
Specifications
| Specification | Standard |
|---|---|
| Materials | Brass (OB), 316 Stainless Steel (OS), Monel (OM) |
| Pipe Sizes | ½″ through 3″ |
| Connection Type | Flange-mounted (wafer style between flanges) |
| Differential Pressure — Brass | 207.6 in H₂O at full-scale flow |
| Differential Pressure — SS/Monel | 276.8 in H₂O at full-scale flow |
| Flow Ranges | 2 GPM (½″ low) to 300 GPM (3″ high) |
| Beta Ratio Range | 0.22 – 0.65 (varies by model) |
| Weight | 2 lbs (½″–¾″), 3 lbs (1″–2″), 4 lbs (2½″), 6 lbs (3″) |
| Flow Nozzle Profile | Convergent curved inlet with cylindrical throat |
| Applications | Liquids, gases, corrosive fluids, high-temperature service |
Model Number Selection Table
All models rated at 207.6 in H₂O (OB brass) or 276.8 in H₂O (OS/OM stainless & Monel) at full-scale flow.
| OB Model | OS Model | OM Model | Lbs | Line Size | Brass (OB) | SS / Monel (OS/OM) | GPM | ||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Bore | Beta | in/H₂O | Bore | Beta | in/H₂O | ||||||
| OB-0.5-1 | OS-0.5-1 | OM-0.5-1 | 2.00 | 1/2" | 0.159 | 0.221 | 207.6 | 0.147 | 0.23 | 276.8 | 2 |
| OB-0.5-2 | OS-0.5-2 | OM-0.5-2 | 2.00 | 1/2" | 0.223 | 0.310 | 207.6 | 0.207 | 0.33 | 276.8 | 4 |
| OB-0.5-3 | OS-0.5-3 | OM-0.5-3 | 2.00 | 1/2" | 0.271 | 0.376 | 207.6 | 0.253 | 0.40 | 276.8 | 6 |
| OB-0.75-1 | OS-0.75-1 | OM-0.75-1 | 2.00 | 3/4" | 0.273 | 0.379 | 207.6 | 0.254 | 0.30 | 276.8 | 6 |
| OB-0.75-2 | OS-0.75-2 | OM-0.75-2 | 2.00 | 3/4" | 0.350 | 0.420 | 207.6 | 0.326 | 0.39 | 276.8 | 10 |
| OB-0.75-3 | OS-0.75-3 | OM-0.75-3 | 2.00 | 3/4" | 0.486 | 0.510 | 207.6 | 0.456 | 0.55 | 276.8 | 20 |
| OB-1.0-1 | OS-1.0-1 | OM-1.0-1 | 3.00 | 1" | 0.428 | 0.400 | 207.6 | 0.400 | 0.38 | 276.8 | 15 |
| OB-1.0-2 | OS-1.0-2 | OM-1.0-2 | 3.00 | 1" | 0.492 | 0.550 | 207.6 | 0.461 | 0.44 | 276.8 | 20 |
| OB-1.0-3 | OS-1.0-3 | OM-1.0-3 | 3.00 | 1" | 0.589 | 0.560 | 207.6 | 0.561 | 0.53 | 276.8 | 30 |
| OB-1.5-1 | OS-1.5-1 | OM-1.5-1 | 3.00 | 1 1/2" | 0.689 | 0.420 | 207.6 | 0.650 | 0.40 | 276.8 | 40 |
| OB-1.5-2 | OS-1.5-2 | OM-1.5-2 | 3.00 | 1 1/2" | 0.848 | 0.530 | 207.6 | 0.791 | 0.49 | 276.8 | 60 |
| OB-1.5-3 | OS-1.5-3 | OM-1.5-3 | 3.00 | 1 1/2" | 1.060 | 0.650 | 207.6 | 1.000 | 0.62 | 276.8 | 100 |
| OB-2.0-1 | OS-2.0-1 | OM-2.0-1 | 3.00 | 2" | 0.854 | 0.410 | 207.6 | 0.796 | 0.38 | 276.8 | 60 |
| OB-2.0-2 | OS-2.0-2 | OM-2.0-2 | 3.00 | 2" | 0.986 | 0.480 | 207.6 | 1.018 | 0.49 | 276.8 | 100 |
| OB-2.0-3 | OS-2.0-3 | OM-2.0-3 | 3.00 | 2" | 1.090 | 0.520 | 207.6 | 1.223 | 0.59 | 276.8 | 150 |
| OB-2.5-1 | OS-2.5-1 | OM-2.5-1 | 4.00 | 2 1/2" | 0.860 | 0.340 | 207.6 | 0.799 | 0.32 | 276.8 | 60 |
| OB-2.5-2 | OS-2.5-2 | OM-2.5-2 | 4.00 | 2 1/2" | 1.090 | 0.440 | 207.6 | 1.026 | 0.42 | 276.8 | 100 |
| OB-2.5-3 | OS-2.5-3 | OM-2.5-3 | 4.00 | 2 1/2" | 1.533 | 0.620 | 207.6 | 1.418 | 0.57 | 276.8 | 200 |
| OB-3.0-1 | OS-3.0-1 | OM-3.0-1 | 6.00 | 3" | 1.100 | 0.350 | 207.6 | 1.063 | 0.35 | 276.8 | 100 |
| OB-3.0-2 | OS-3.0-2 | OM-3.0-2 | 6.00 | 3" | 1.580 | 0.510 | 207.6 | 1.510 | 0.49 | 276.8 | 200 |
| OB-3.0-3 | OS-3.0-3 | OM-3.0-3 | 6.00 | 3" | 1.900 | 0.620 | 207.6 | 1.822 | 0.59 | 276.8 | 300 |
Installation Guidelines
- Straight Pipe: Provide a minimum of 10 pipe diameters upstream and 5 diameters downstream of unobstructed straight pipe.
- Flange Taps: Standard flange taps are located 1″ upstream and 1″ downstream of the orifice plate face.
- Impulse Lines: Slope liquid-service impulse lines upward to the transmitter to prevent gas pockets; slope gas-service lines downward to prevent liquid accumulation.
- Orientation: Orifice plates may be installed in horizontal, vertical, or inclined pipe — ensure the drain/vent hole is correctly positioned per service type.
- Flow Nozzle: For abrasive or erosive fluids, specify the flow nozzle profile to extend service life and maintain measurement accuracy.
Orifice Plate FAQ
Common questions about selecting, sizing, and installing RCM Industries orifice plates.
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