The LM300 Series lube level maintainer is a float-operated instrument that continuously monitors crankcase oil and automatically replenishes it from a makeup supply reservoir before the level falls outside the normal operating band. Built-in SPDT snap-acting switches on most models deliver configurable alarm and shutdown protection — triggering on low oil level, low-low level, or overfill conditions — keeping engines, compressors, and pumps protected without constant operator attention.
The LM300 Series Level Maintainer is a rugged, float-operated device designed to automatically add oil to a crankcase or reservoir whenever the lube level falls below the normal operating range. Housed in a die-cast aluminum enclosure, most models include factory-integrated switches that trigger an alarm and/or shut down the equipment if the makeup oil supply is exhausted or if oil accumulates beyond the safe upper limit. The LM300 is widely used across gas compression, power generation, and industrial pumping applications where consistent lubrication is critical. Explosion-proof (EX) variants carry CSA certification for Class I, Division 1 hazardous area service, extending the product's reach into demanding upstream oil and gas environments.
Key technical parameters for the LM300 Series Level Maintainer are listed below for engineering reference and procurement use. Specifications apply across the standard model range unless otherwise noted.
| Parameter | Specification |
|---|---|
| Case / Cover Material | Die Cast Aluminum |
| Switch Housing Material | Aluminum |
| Float Material | Rigid Polyurethane Foam; Polyurethane Coated |
| Max. Ambient Temperature | 250°F (121°C) |
| Oil Inlet Connection | 1/2-14 NPT (Top Entry) with Built-In Removable Filter Screen |
| Outlet Connection | 3/4-14 NPT — Left Side, Right Side, and Bottom |
| Crankcase Balance Vent Fitting | 1/2-14 NPT |
| Inlet Orifice — Standard | 1/4 in. (6 mm) |
| Inlet Orifice — Optional | 1/8 in. (3 mm) |
| Orifice Seal | Buna-N Thumb-Valve |
| Max. Inlet Pressure — 1/8 in. Orifice | 30 psi (207 kPa) [2.07 bar] |
| Max. Inlet Pressure — 1/4 in. Orifice | 15 ft oil head (4.6 m oil) |
| Max. Differential (Running vs. Stationary) | 2 in. (51 mm) |
| Max. Case Pressure (MCP) | 15 psi (103 kPa) [1.03 bar] |
| Switch Contact Type | Silver, SPDT Snap-Acting |
| Switch Contact Rating | 10 A @ 125/250 VAC; 10 A @ 30 VDC |
| Switch Wire (Switch Models) | 18 AWG × 13 in. (1.0 mm² × 330 mm) |
| Approval Rating | All CSA Certified — Switch Contacts 10 A @ 250 VAC |
| LM301–LM305 Certification | CSA Non-Hazardous Locations, Enclosure Type 4 |
| LM301-EX–LM303-EX Certification | CSA Class I, Groups C & D; Class II, Groups F & G; Enclosure Type 4 |
| Flow Rate — 1/4 in. Orifice (SAE 30 @ 32°F) | 4.7–31.0 GPH (17.8–117.3 LPH) at 4–15 ft oil head |
| Flow Rate — 1/8 in. Orifice (SAE 30 @ 32°F) | 16.9–32.1 GPH (63.7–121.5 LPH) at 10–30 psig |
| Lens Type | Clear Frog Eye — High-Impact, UV-Stabilized, High-Temp Nylon |
| Glass Lens Option | Available on LM301 and LM301-EX Models |
| Mounting | Compatible with Pipe Bracket or Universal Bracket |
| Enclosure Height — Non-EX Models | 7 in. (178 mm) |
| Enclosure Width — Non-EX Models | 7-7/8 in. (200 mm) |
| Shipping Weight — Non-EX | 6 lbs. 6 oz. (2.89 kg) |
| Shipping Weight — EX | 6 lbs. 12 oz. (3.06 kg) |
| Shipping Dimensions | 10-5/8 × 8-7/8 × 6-3/4 in. (270 × 225 × 171 mm) |
The LM300 Series Level Maintainer operates on a straightforward float-controlled valve principle. A polyurethane-coated rigid foam float inside the unit body rises and falls with the crankcase oil level. When the oil level is within the normal operating range, the float holds the inlet valve closed, preventing additional oil from entering. As the engine or compressor consumes or loses oil and the level drops, the float descends and opens the inlet orifice, allowing makeup oil to flow from the supply reservoir into the crankcase until the correct level is restored.
On switch-equipped models, the float mechanism simultaneously actuates SPDT snap-acting switch contacts. If the makeup oil supply runs out and the level continues to fall below the minimum threshold, the switch triggers a configurable alarm output, a full equipment shutdown signal, or both — depending on the model variant selected. High-level protection is available on LM302 and LM303 models, which incorporate a second switch to detect overfill conditions and trigger a corresponding alarm or shutdown response.
A crankcase balance vent fitting maintains equal pressure between the maintainer body and the engine crankcase, ensuring the float responds accurately to actual oil level rather than pressure-induced displacement. The onboard Test Knob lets technicians manually simulate low-level and high-level conditions to verify that connected alarm and shutdown circuits are functioning correctly — without requiring the equipment to actually reach those states during testing.
The LM300 Series automatically adds oil to the crankcase whenever the lube level drops below the normal operating range. Built-in switches on most models trigger an alarm or shut down the equipment if the makeup oil supply runs out or if an overfill condition is detected — protecting engines, compressors, and pumps without constant operator monitoring.
Yes. The LM301-EX through LM303-EX models are CSA certified for Class I, Groups C and D and Class II, Groups F and G hazardous locations, with Enclosure Type 4 certification. Standard LM301 through LM305 models are CSA certified for non-hazardous locations. Consult the relevant installation diagrams when integrating switch models with an approved controller in classified areas.
The LM300 Series is designed for use on engines, compressors, pumps, and coolers — any industrial equipment with a crankcase or oil reservoir that requires continuous level management during operation. It is widely deployed on gas compression trains, stationary power generation sets, and skid-mounted pumping equipment across oil and gas, marine, and power industries.
The LM300 includes a built-in Test Knob. Rotating it clockwise simulates a low-level condition to test the alarm or shutdown circuit; rotating counterclockwise tests the high-level switch. This in-place test function eliminates the need to drain oil or interrupt equipment operation during routine switch function checks, simplifying maintenance program compliance.
The standard 1/4 in. (6 mm) orifice is appropriate for gravity-feed systems with an oil supply head between 4 ft and 15 ft, handling 4.7 to 31.0 GPH (SAE 30 at 32°F). If your makeup oil supply is pressurized at 10–30 psi, specify the 1/8 in. (3 mm) orifice option, which delivers 16.9 to 32.1 GPH under those conditions. Selecting the correct orifice ensures flow rate is properly matched to your supply arrangement.
Both LM302 and LM303 include two SPDT switches for combined low-level and high-level alarm or shutdown protection. The difference is the switch wiring configuration: LM302 contacts are wired normally-open (N.O.) in the normal operating range, while LM303 contacts are wired normally-closed (N.C.). The choice between N.O. and N.C. depends on the fail-safe logic required by the connected control system or safety relay.
Our engineers will recommend the right LM300 Series model for your specific application, send you the full technical datasheet, and provide a competitive quote.
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