Cracking the Code: A Guide to Murphy Swichgage® Model Numbers
Published on
March 20th, 2026
In the world of industrial engine protection, there is one name that stands above the rest: the Murphy Swichgage®. These aren't just gauges; they are rugged, high-end insurance policies for your most expensive equipment.
Whether it’s a massive irrigation pump in the Central Valley or a backup generator for a hospital, Murphy by Enovation Controls has set the standard for durability. These instruments are famous for outlasting the engines they protect—often running for decades in the harshest vibration, heat, and weather conditions.
As an authorized distributor, MurCal doesn't just sell these parts; we live and breathe them. But we know that looking at a model number like A25T-160-10-1/2 can feel like trying to crack a secret code.
The "Secret Code": Breaking Down the Model Numbers
Every letter and number in a Murphy model string tells a specific story about what the gauge does and what it’s made of.
1. The First Letter: The Case Material
-No Letter (e.g., 20P): This indicates a Steel Case. These are the classic, heavy-duty models.
-"A" (e.g., A25T): This stands for the A-Series. These feature a glass-filled polycarbonate case and are "Environmentally Sealed" with O-rings. They are ideal for corrosive environments where rust or moisture ingress is an issue.
2. The First Two Numbers: The Dial Size
-20: A 2-inch (51 mm) dial.
-25: A 2.5-inch (64 mm) dial.
-45: A 4.5-inch (114 mm) dial (typically seen in the OPL series).
3. The Function Letters: What are we measuring?
This is the heart of the code.
-P: Pressure (Standard)
-DP: Differential Pressure (Measures the "drop" across a filter)
-V: Vacuum
-VWC: Vacuum Water Column (Specifically for air filter restriction)
-T: Temperature (Vapor Actuated)
-BTG: Bimetallic Temperature (Often for exhaust or cylinder head temp)
4. The Suffixes: Extra Features
-F: Denotes an "FS" Contact (an isolated internal contact) or, in larger models, a Front Flange for panel mounting.
-E: Denotes a "Snap-Acting" internal switch (SPDT) rather than the standard pointer-to-contact style.
-OS:Oil Sealed (Liquid filled) for extreme vibration environments.
5. The End Numbers: Reach and Fit
The final numbers in a string (usually found on temperature gauges) tell you how far the sensor reaches and how it connects to the engine.
-The Length: For T (Temperature) models, this number is the length of the flexible Capillary Tube in feet. For BTG (Bimetallic) models, this number refers to the Rigid Stem length in inches.
-The Thread: A fraction like 1/2 or 1/4 refers to the NPT thread size of the connection bulb or adapter. This ensures the gauge actually fits into your engine block or pipe.
Real-World Examples Decoded
-20P-F-75: This is a 2-inch, Steel Case, Pressure Swichgage with "FS" Contact anda range of 0-75 PSI. You’ll see these on almost every diesel engine for oil pressure.
-20VWC-30: This is a 2-inch, Vacuum gauge measured in Inches of Water Column (0-30 range). This is your "Air Filter Restriction" gauge. When it hits 30, it’s time to change that filter!
-A25T-160-10-1/2: A Polycarbonate (A), 2.5-inch (25), Temperature (T) gauge with a 160°F range, a 10-foot capillary, and a 1/2" NPT connection.
-20BTG-220-4-1/2: A 2-inch, Bimetallic (BTG) temperature gauge. These use a rigid stem rather than a flexible tube. This one has a 220°F range, a 4-inch stem, and a 1/2" NPT connection.
Origins and Fun Facts
-The Simple Start: In 1939, Frank W. "Pat" Murphy founded the original company after seeing too many customers lose expensive engines to simple oil and temperature failures.
-The Tattletale®: Introduced in the 1950s, this clever little flag-drop annunciator was the first way an operator could walk up to a stopped engine and see exactly which gauge triggered the shutdown.
-Zero Power Needed: Most Murphy Swichgages are purely mechanical. They use physics (like diaphragms and vapor pressure) to work, meaning they can protect your engine even if the battery is dead or the electronics fail.
-Built-in "Pulsation Dampener": Many pressure models have a tiny internal brass screw that keeps the needle from fluttering—ensuring a smooth, accurate reading even on high-vibration equipment.
The MurCal Advantage
At MurCal, we’ve been working with these gauges since the 1950s. We don't just "box and ship" them—we understand the calibration and exactly how to fit them to your application. We also stock mounting brackets and light kits to make sure your installation is professional and easy to read in the dark.
If you want the legendary reliability of a Murphy Swichgage®, MurCal.com is the place to get it. We love these things because they simply work—yesterday, today, and for the next 30 years.
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Cracking the Code: A Guide to Murphy Swichgage® Model Numbers
In the world of industrial engine protection, there is one name that stands above the rest: the Murphy Swichgage®. These aren't just gauges; they are rugged, high-end insurance policies for your most expensive equipment. Whether it’s a massive irrigation pump in the Central Valley or a backup generator for a hospital, Murphy by Enovation Controls has set the standard for durability. These instruments are famous for outlasting the engines they protect—often running for decades in the harshest vibration, heat, and weather conditions.