What pressure ranges are available for the OPL Series?

OPL Series instruments are available in a wide range of pressure spans, from compound vacuum-pressure ranges (such as 30 in. Hg vacuum to 15 psi) through to high-pressure ranges up to 20,000 psi for demanding industrial applications. The appropriate bourdon tube material and connection size are selected based on the pressure range required.

What sensing element materials are available for the OPL Series?

The OPL Series is available with either a Grade A phosphor bronze bourdon tube with a brass socket, or a full 316 stainless steel bourdon tube and socket for applications involving corrosive media or higher pressure ranges. The stainless steel option is recommended for sour gas, chemical, or seawater service environments.

What is a pulsation dampener and when is it needed with the OPL Series?

A pulsation dampener is a flow-restricting accessory installed in the process connection to reduce rapid pressure fluctuations reaching the bourdon tube and pointer. It is strongly recommended when the OPL Series is used on reciprocating pumps or compressors, where pulsating pressure can cause pointer flutter, erratic limit switch contact, and premature wear of the geared movement.

OPL Series 4-1/2 inch pressure gage with adjustable high low limit switches for engine and compressor control

OPL Series Pressure Gage

4-1/2 in. Dial | Limit Switches | Weatherproof

Pressure Monitoring · Engine Protection · Industrial Control

OPL Series Pressure Gage – 4-1/2 in. Dial with Adjustable High/Low Limit Switches

The OPL Series is a 4-1/2 in. (114 mm) combination pressure indicating gage with integrated adjustable high and low limit switches. Designed for direct wiring into alarm, shutdown, and start-stop pilot circuits, it provides both continuous pressure readout and automatic switching action in a single weatherproof instrument — available in surface mount and panel mount configurations to suit a wide range of engine, compressor, and pump control applications.

4-1/2" Dial Size

2-1-2 Accuracy

SPDT Contacts

IP Weatherproof

Key Features

The OPL Series pressure gage delivers both visual pressure indication and active process protection in a single compact instrument. With a clearly readable 4-1/2 in. dual-scale dial and front-accessible limit switch adjustment knobs, operators can monitor system pressure and configure alarm or shutdown setpoints without removing the instrument from service. The die-cast aluminum weatherproof enclosure, stainless steel geared movement, and self-cleaning limit contacts make the OPL Series a dependable long-term solution for engine protection, compressor monitoring, and pump control across oil and gas, marine, and general industrial environments. Multiple model variants, sensing element materials, process connection sizes, and pressure ranges allow the OPL Series to be precisely matched to a broad range of service conditions.

Combination Pressure Indication and Limit Switching: The OPL Series integrates a precision bourdon tube pressure gage with independently adjustable high and low limit switch contacts in a single instrument. When system pressure reaches either setpoint, the pointer physically contacts the limit arm to complete the pilot circuit — triggering alarm, shutdown, or start-stop action without any separate electronic transmitter or controller. This direct mechanical switching arrangement ensures reliable operation even in environments where electronic control systems are not available or practical.
Front-Accessible Limit Switch Adjustment: Both high and low limit switch setpoints can be adjusted directly from the front face of the instrument without disassembly or tools. This allows field operators to change alarm or shutdown thresholds quickly during commissioning or process changes, reducing downtime and simplifying setup. The adjustable contacts are clearly visible through the optically clear polycarbonate lens, allowing setpoint positions to be verified at a glance.
Self-Cleaning Limit Contacts: The limit switch contacts incorporate a self-cleaning wiping motion each time the pointer makes or breaks the circuit. This mechanical action removes surface oxides and contamination from the contact faces during normal operation, maintaining reliable electrical continuity over extended service periods — particularly important in environments where infrequent switching could otherwise allow contact deterioration between operations.
Weatherproof Die-Cast Aluminum Enclosure: The instrument housing is constructed from die-cast aluminum and rated for weatherproof service, providing effective protection against rain, condensation, and airborne contaminants in outdoor or partially sheltered installations. Optional environmentally sealed (ES) and oil-sealed (OS) versions further extend protection for harsher exposure conditions. An explosion-proof (EX) enclosure option is available for Class I, Division 1 hazardous area installations.
4-1/2 in. Dual-Scale Dial for Easy Reading: The 114 mm white-on-black dial provides clear, easy-to-read pressure indication from a distance. All dials are dual-scaled in both psi and kPa as standard, eliminating unit conversion confusion in multi-discipline environments. The high-visibility pointer includes a calibration hub for precise zero and span adjustment during commissioning or recalibration.
Stainless Steel Geared Movement: The internal geared movement uses 302 and 304 stainless steel components throughout, providing strong resistance to corrosion from condensation and process vapours that can penetrate even weatherproof enclosures over time. The stainless movement also exhibits lower thermal expansion than brass alternatives, helping maintain calibration accuracy across a wider ambient temperature range.
Choice of Bourdon Tube Materials and Connection Sizes: The OPL Series is available with either a Grade A phosphor bronze C-tube with brass socket for general service applications, or a full 316 stainless steel bourdon tube and socket for service involving corrosive media, sour gas, or higher pressure ranges up to 10,000 psi. Process connections are available in both 1/4 NPT and 1/2 NPT to suit standard piping arrangements across a wide range of equipment.

Applications

Engine Oil Pressure Monitoring and Shutdown: Low engine oil pressure is one of the leading causes of catastrophic engine failure in unattended industrial applications. The OPL Series, installed in the engine lubricating oil circuit, continuously indicates oil pressure while the low limit contact triggers an automatic shutdown when pressure drops below the safe operating threshold — protecting expensive engine assets from lubrication failure damage.
Compressor Suction and Discharge Pressure Control: Reciprocating and rotary compressors require accurate pressure monitoring at both the suction and discharge sides of the compression circuit. The OPL Series provides direct pressure readout alongside high and low limit switching for alarm and shutdown functions, making it suitable for compressor protection panels in gas gathering, processing, and distribution applications.
Pump Discharge Pressure Monitoring: Industrial pump systems require overpressure protection to prevent piping and equipment damage when downstream valves close unexpectedly or flow becomes restricted. The OPL Series high limit contact can be wired to shut down the pump motor or activate a bypass valve when discharge pressure exceeds the allowable setpoint, providing a reliable first line of overpressure defence.
Hydraulic System Pressure Indication and Alarm: Hydraulic power units and actuator circuits require continuous pressure monitoring to verify system integrity and detect developing leaks or relief valve malfunctions. The OPL Series provides field operators with a clear local pressure indication alongside automatic alarm activation when pressure falls outside acceptable operating limits.
Control Panel Integration for Compressors and Pump Skids: The OPLFC panel mount model is designed specifically for integration into compressor control panels, pump skid electrical enclosures, and engine control stations. Its flush panel mounting arrangement and pigtail wire termination simplify integration into existing panel layouts, while the front-accessible limit adjustment knobs remain accessible without opening the panel door.
Engine and Motor Start-Stop Circuits: In applications where equipment must start automatically when process pressure drops below a minimum level and stop when pressure reaches an upper limit — such as pressure-fed lubrication systems or gas boost compressors — the OPL Series limit contacts can be wired directly into the motor starter or engine control circuit to provide fully automatic start-stop pressure regulation without additional instrumentation.

Technical Specifications

OPL Series instruments are available in surface mount (OPLC) and panel mount (OPLFC / OPLFG) configurations across a wide range of pressure spans and sensing element materials. Key specifications are listed below for engineering reference and procurement purposes.

Parameter	Specification
Dial Size	4-1/2 in. (114 mm)
Dial Display	White on black; dual-scaled psi and kPa
Gage Accuracy	2-1-2; ±2% first and last quarters of scale, ±1% middle half
Case Material	Die-cast aluminum; weatherproof
Lens Material	Optically clear polycarbonate
Geared Movement	302 and 304 stainless steel
Pointer	High visibility; pointer calibration hub included
Sensing Element	Bronze bourdon tube (brass socket) or 316 stainless steel bourdon tube and socket
Process Connection	1/4 NPT or 1/2 NPT
Contact Type (OPLC & OPLFC)	1 SPDT; center off; 2 A, 30 VDC / 0.1 A, 125 VAC pilot duty
Relay Contacts (OPLC & OPLFC)	SPDT dry relay contacts; 10 A, 125 VAC
Pressure Ranges	30 in. Hg vacuum–15 psi compound to 20,000 psi (range-dependent on tube material and size)
Available Models	OPLC (surface mount with low-limit lockout); OPLFC (panel mount); OPLFG (panel mount, indication only)
Hazardous Area Options	Explosion-Proof (Class I, Div. 1, Groups C & D); Non-Incendive; Intrinsically Safe
Enclosure Options	Standard weatherproof; Environmentally Sealed (ES); Oil-Sealed (OS); Explosion-Proof (EX)
Certifications	CSA Listed (selected configurations); UL Listed (selected configurations); CE marked; EMC Directive 89/336/EEC compliant
Shipping Weight – OPLC	5 lbs 9 oz (2.5 kg)
Shipping Weight – OPLFC / OPLFG	3 lbs 4 oz (1.5 kg)
Shipping Dimensions – OPLC	9-1/2 × 9-1/4 × 5-3/4 in. (241 × 235 × 146 mm)
Shipping Dimensions – OPLFC / OPLFG	9-1/4 × 8-1/4 × 5-1/2 in. (235 × 210 × 140 mm)

How the OPL Series Pressure Gage Works

The OPL Series operates on the well-established bourdon tube principle, combined with direct mechanical limit switching to deliver both pressure indication and process control in a single instrument. When pressurised fluid enters through the process connection, it acts on the interior of the curved bourdon tube. As internal pressure increases, the tube tends to straighten, and this deflection is converted into rotary pointer movement through a precisely geared stainless steel movement assembly. The result is a continuously updated pressure reading on the 4-1/2 in. dual-scale dial.

Within the dial face, two independently adjustable limit arms — one for the high setpoint and one for the low setpoint — are positioned at the desired alarm or shutdown pressure values using the external adjustment knobs on the front of the instrument. As process pressure changes and the pointer moves across the dial, physical contact between the pointer and either limit arm completes the electrical pilot circuit. This closing action activates whatever control function is wired to the contact terminals: an alarm annunciator, a solenoid-operated shutdown valve, an engine ignition cutout, or a motor starter — depending on the application.

The self-cleaning wiping motion of the contacts during each make-and-break cycle ensures consistent electrical continuity is maintained even after extended periods between switching events. For installations subject to pulsating pressure from reciprocating equipment, a pulsation dampener accessory fitted at the process connection smooths pressure fluctuations before they reach the bourdon tube, preventing pointer flutter and protecting both the geared movement and the limit contacts from premature wear.

Technical FAQ

Common Questions Answered

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The OPL Series is a combination pressure indicating gage and limit switch instrument used to monitor system pressure and trigger alarm, shutdown, or engine start-stop actions when pressure rises above or falls below set thresholds. It is widely used on engines, compressors, and pump systems across oil and gas, marine, and industrial applications where both local pressure readout and automatic protective switching are required in a single instrument.

The OPLC is a surface mount gage instrument with adjustable high and low limit switches and an integrated low-limit lockout toggle switch for equipment startup. The OPLFC is a panel mount version with the same limit switch functionality, but the low-limit lockout is handled externally through the control circuit — making it the preferred choice for compressor and pump control panels. The OPLFG is a panel mount indicating-only gage instrument with no limit switch contacts, used where local pressure readout is required without switching action.

OPL Series instruments are available across a broad range of pressure spans, from compound vacuum-pressure ranges (such as 30 in. Hg vacuum to 15 psi) through to high-pressure ranges reaching 20,000 psi for demanding industrial service. The appropriate bourdon tube material, tube type, and process connection size are determined by the pressure range required. Bronze C-tube construction covers ranges through 1,000 psi; stainless steel drawn helical tube construction is used for ranges from 1,500 to 10,000 psi.

Yes. Selected OPL Series configurations are available with an Explosion-Proof (EX) enclosure rated for Class I, Division 1, Groups C and D hazardous locations. Division 2 applications can also be addressed through Non-Incendive or Intrinsically Safe system configurations. Contact our technical team with your area classification details to confirm the appropriate model and option code for your specific installation.

For general service with non-corrosive fluids and pressures up to 1,000 psi, the Grade A phosphor bronze bourdon tube with a brass socket is a cost-effective and well-proven choice. For applications involving corrosive media, sour gas, produced water, seawater, or process fluids incompatible with brass — or for higher pressure ranges — the full 316 stainless steel bourdon tube and socket is recommended. If in doubt, our engineers can advise on the correct material selection for your specific process fluid and pressure conditions.

A pulsation dampener (Part No. 05000610, ordered separately) is strongly recommended whenever the OPL Series is installed on reciprocating pumps or compressors that generate cyclic pressure fluctuations in the process line. Without dampening, pointer flutter caused by pulsating pressure can cause erratic limit switch contact, inaccurate pressure indication, and accelerated wear of the internal geared movement. The dampener is available in brass, carbon steel, and stainless steel to suit various process fluid compatibility requirements.