The Fisher MR98 Series represents a versatile line of direct-operated regulators designed for liquid, gas, air, and steam applications. These units are engineered to maintain upstream pressure (backpressure regulation), provide overpressure protection (relief), or manage specific pressure gaps (differential relief). Their robust construction makes them the industry standard for everything from tank blanketing to high-pressure fuel systems.
01 Technical Model Overview and Capabilities
The MR98 Series is divided into seven distinct models categorized by pressure range and control logic.
| Model | Function | Relief Set Range | Body Size Options |
| MR98L | Low-Pressure Backpressure / Relief | 2 to 38 psig (0.14 to 2.6 bar) | 1/4 NPT to 1 inch |
| MR98H | Medium-Pressure Backpressure / Relief | 5 to 200 psig (0.34 to 13.8 bar) | 1/4 NPT to 2 inches |
| MR98HH | High-Pressure Backpressure / Relief | 150 to 375 psig (10.3 to 25.9 bar) | 1/4 NPT to 1 inch |
| MR98LD | Low-Pressure Differential Relief | 2 to 38 psi (0.14 to 2.6 bar) | 1/4 NPT to 1 inch |
| MR98HD | Medium-Pressure Differential Relief | 5 to 200 psi (0.34 to 13.8 bar) | 1/4 NPT to 2 inches |
| MR98HDP | Differential Relief w/ Remote Setpoint | 5 to 200 psi (0.34 to 13.8 bar) | 1/4 NPT to 2 inches |
| MR98HHD | High-Pressure Differential Relief | 150 to 375 psi (10.3 to 25.9 bar) | 1/4 NPT to 1 inch |
02 Core Design and Engineering Features
The reliability of the Fisher MR98 Series stems from its direct-acting, spring-loaded architecture.
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Immediate Response: Since the units are direct-acting, they react instantly to pressure changes without the delay associated with pilot-operated systems.
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Pressure Loading (D Models): Models like the MR98HD utilize external pressure loading on the diaphragm. This allows the valve to maintain a constant differential pressure across equipment (such as filters) or to have its setpoint adjusted remotely.
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High Performance Internals:
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Metal Seats: Rated for ANSI/FCI Class IV shutoff.
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Elastomer Seats: Rated for ANSI/FCI Class VI shutoff, ideal for applications requiring bubble-tight closure.
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Material Versatility: Body options range from Gray Cast Iron and WCC Carbon Steel to CF8M/CF3M Stainless Steel, Monel, and Hastelloy C, ensuring compatibility with corrosive media or extreme temperatures.
03 Operational Principles
Backpressure and Relief (MR98L/H/HH)
These valves respond to changes in upstream pressure. Pressure registers under the diaphragm via an internal port. When the upstream pressure exceeds the force of the compressed spring, the diaphragm moves upward, lifting the valve plug off the orifice. This opens the flow path to vent excess pressure.
Differential Relief (MR98D Series)
These models maintain a constant pressure difference between the controlled pressure and a loading pressure. As the loading pressure on the upper diaphragm increases, it moves the valve plug closer to the orifice to restrict flow. If loading pressure decreases, the plug moves away, allowing higher flow to maintain the required ΔP.
04 Common Industrial Applications
The Fisher MR98 Series is essential in systems where precise pressure containment is a safety requirement:
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Fuel Supply Systems: Maintaining constant backpressure in fuel lines for burners, turbines, and large industrial engines.
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Pump Bypass: Protecting pumps from overheating by allowing recirculation when downstream demand is low.
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Filter and Heat Exchanger Protection: Using the D series to prevent damage caused by excessive pressure drops across sensitive equipment.
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API Lube Oil Systems: Providing reliable overpressure relief in lubrication systems for rotating machinery.
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Sterilizers and Autoclaves: Managing critical steam pressure differentials in pharmaceutical and food processing plants.
05 Procurement and Technical Support
Correct model selection for the Fisher MR98 Series requires careful consideration of the Flow Coefficient (Cv), spring range, and material compatibility. Xi’an Yunrui Trading Co., Ltd. (Yunrui) assists industrial clients in the technical verification and procurement of 100% genuine Fisher hardware.
Our technical support includes calculating the required spring range to ensure the valve operates within its most stable band. By maintaining strategic stock of MR98L and MR98H units in the Xi’an warehouse, we provide rapid delivery to critical projects. Specialized logistics services ensure that all international orders include the necessary material certificates and factory documentation for seamless customs clearance and site commissioning.
