The MLS Series liquid level switch is a float-activated instrument that triggers an electrical SPDT reed switch to signal high or low liquid levels in demanding gas compressor scrubber environments. Constructed from 304 stainless steel, rated to 2000 psi (13.8 MPa), and certified for CSA Class I, Division 1 hazardous locations, the MLS Series provides dependable level detection without seals to fail — offering engineers a robust, maintenance-friendly solution for annunciation, shutdown, or PLC input across gas compression and processing facilities.
The MLS Series liquid level switch is purpose-engineered for the rigours of gas compressor scrubber service, where pressure ratings, material integrity, and reliable switching are non-negotiable. Using a 304 stainless steel float to activate a magnetically coupled SPDT reed switch, the MLS eliminates mechanical seals from the design entirely — removing one of the most common failure points in high-pressure liquid level switches. It screws directly into the scrubber wall or mounts via an external float chamber, supports both rising and falling liquid detection without body rotation, and is available in 1½ and 2 in. NPT configurations with or without an integrated push-button test facility. With CSA Class I Division 1 certification covering Groups B, C, and D, the MLS Series is a proven choice wherever hydrocarbons, H₂S, or other flammable gases may be present.
The MLS Series is available in 1½ in. NPT (MLS-015) and 2 in. NPT (MLS-020) configurations, each with or without an integrated push-button test function. All key parameters are listed below for engineering reference and procurement use.
| Parameter | Specification |
|---|---|
| Switch Type | SPDT Reed Switch (Form C) |
| Electrical Rating | 30 VAC/VDC, 75 mA |
| Actuation Principle | Float-activated magnetic reed switch |
| Process Connection | 1½ in. NPT (MLS-015); 2 in. NPT (MLS-020) |
| Electrical Conduit Entry | ½ in. NPT |
| Working Pressure | 2000 psi (13.8 MPa) [138 bar] |
| Process Temperature Range | -20° to 300° F (-29° to 149° C) |
| Minimum Fluid Specific Gravity | 0.50 (no float extension); 0.65 (with 1 in. float extension) |
| Body Material | ASTM A351 CF8 (304 Stainless Steel) |
| Cover Material | ASTM A351 CF8 (304 Stainless Steel) |
| Float Material | 304 Stainless Steel |
| Other Wetted Parts | 303, 304, and 316 Stainless Steel |
| Conductor Size (Minimum) | 26 AWG |
| Conductor Size (Maximum) | 16 AWG |
| Hazardous Area Certification | CSA C/US Class I, Division 1, Groups B, C & D |
| Safety Standard Compliance | ANSI/ISA 12.27.01 (Single Seal) |
| Canadian Registration | OF12013.2 C (All Provinces and Territories), CSA Approved |
| Construction | Seal-free; clean magnet design |
| Trip Direction | Rising and falling (no body rotation required) |
| Optional Feature | Push-button test function (TF models) |
| Approx. Shipping Weight (MLS-015) | 5 lbs. (2.27 kg) |
| Approx. Shipping Weight (MLS-020) | 5.5 lbs. (2.49 kg) |
| Shipping Dimensions | 14 × 5 × 3.5 in. (356 × 127 × 89 mm) |
The MLS Series operates on a straightforward float-and-magnet principle that is inherently well-suited to high-pressure service. A 304 stainless steel float is suspended inside the scrubber vessel or external float chamber, buoyed by the liquid present at the switch's installed elevation. As liquid level rises and the float lifts, a permanent magnet housed within or attached to the float assembly passes into proximity with a hermetically sealed SPDT reed switch located in the switch body. The magnetic field causes the reed switch contacts to change state — from one pole to the other — generating the output signal that is transmitted to a remote annunciator, controller, or PLC.
When liquid level drops and the float descends, the magnet moves away from the reed switch, and the contacts return to their original state. Because the reed switch contacts are enclosed in a sealed glass envelope and are actuated magnetically rather than mechanically, there is no requirement for a dynamic process seal between the fluid-wetted float mechanism and the electrical switch chamber. This seal-free approach is a key reliability advantage in high-pressure, cyclic-pressure applications where conventional elastomeric seals are subject to fatigue and leakage over time.
The clean magnet design minimises ferrous debris accumulation, preserving consistent actuation across the service life of the switch. On TF-model variants, the push-button test facility allows operators to manually simulate float movement and verify the complete signal path from switch to panel without altering actual process conditions — providing confidence in system readiness without requiring process interruption.
The MLS Series is designed specifically for liquid level detection in high-pressure gas compressor scrubbers and similar process vessels. It generates a pilot signal via an SPDT reed switch to indicate high or low liquid levels to an annunciator, controller, or PLC. The switch can also be used with an external float chamber for applications where direct vessel mounting is not preferred.
The MLS Series is rated to a working pressure of 2000 psi (13.8 MPa / 138 bar). This rating covers the operating pressures found in most natural gas compression and processing equipment. It is essential to avoid exceeding the rated pressure, as doing so can permanently deform the stainless-steel float, changing its buoyancy characteristics and impairing reliable switch operation.
Without a float extension, the MLS Series operates in fluids with a specific gravity of 0.50 or higher — covering a wide range of hydrocarbon liquids and water. When a 1-inch float extension is used, the minimum specific gravity increases to 0.65. Operators should verify that the process fluid density is within the supported range to ensure reliable float actuation under all operating conditions.
Yes. The MLS Series carries CSA C/US certification for Class I, Division 1, Groups B, C, and D hazardous locations — covering the flammable gas and vapour environments typical of oil and gas compression and processing facilities. It is also ANSI/ISA 12.27.01 compliant as a Single Seal device and is Canadian registered (OF12013.2 C) for use across all provinces and territories. Note that the unit is not recommended for hydrogen gas applications despite the Group B rating encompassing some similar environments.
The integrated test button on MLS-015-TF and MLS-020-TF models allows maintenance personnel to perform a complete end-to-end functional check of the level switch and its associated wiring without changing the actual liquid level in the process vessel. The test confirms that the float mechanism moves freely, that the magnet correctly actuates the reed switch, and that the signal circuit from the switch to the remote control panel or annunciator is intact and correctly wired — all in a single test action.
Yes. All MLS Series models are compatible with a dedicated external float chamber accessory, in addition to direct scrubber wall mounting. The external float chamber connects to the process vessel through equalising connections, allowing the switch to sense internal vessel liquid levels while being physically mounted outside the vessel wall. This configuration is preferred where vessel penetrations need to be minimised, where maintenance access is a consideration, or where existing vessel nozzle configurations are not suited to direct switch installation.
Our engineers will recommend the right MLS Series model for your scrubber or process vessel application, provide the full technical datasheet, and deliver a competitive quote.
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