For tank farm operators, petroleum terminal engineers, floating-roof tank maintenance teams, and EPC specifiers who require reliable high-level and overfill protection on internal and external floating-roof storage tanks, the Omnitrol 621/721 Series delivers rugged, mechanically-actuated level switching using dense lead displacers on stainless-steel beaded chain.
Designed for hazardous environments, it installs easily from the tank top without product intrusion — making it a trusted mechanical safeguard for terminals, refineries, and midstream operators.
Immune to wind, turbulence, and roof bounce — ensures accurate switching on floating-roof tanks.
No wetted electrical components; all mechanics outside product for safer access and maintenance.
621 for one alarm point; 721 for Hi / Hi-Hi redundancy.
Prevents tangling, stretching, or kinking — built for long-term field durability.
Suitable for Class I Groups B, C, D and Class II Groups E, F, G installations.
Ideal for alarm applications
Set to specific gravity — unaffected by temperature or pressure cycling.
The Omnitrol 621/721 uses a weighted lead displacer suspended on a stainless-steel beaded chain. As a floating tank roof rises, the chain lifts the displacer until it actuates a positive mechanical snap-action switch, ensuring definitive alarm travel.
This design solves a persistent problem in floating-roof tanks: false alarms caused by wind, vibration, or slosh. The displacer’s mass keeps it stable until the roof reaches the certified alarm height — making it ideal for external floating roofs, internal pans, and tanks subject to weather forces.
With top-mount installation, the device does not penetrate the tank roof, so there is no process breach, simplifying maintenance and improving worker safety.
| Parameter | Specification |
|---|---|
|
Models |
621 (single-stage), 721 (dual-stage alarms) |
|
Sensing Method
|
Weighted lead displacer w/ stainless beaded chain |
|
Mounting |
2½″ NPT or flanged top-mount |
|
Housing Options |
WR or Explosion Proof/Vapor Proof/ Rain Tight |
|
Temperature Range |
–20 °F to +400 °F (–29 °C to +204 °C) |
|
Switch Types |
SPDT / DPDT Micro Switches |
|
Power Requirements |
None (mechanical actuation) |
|
Certifications |
UL & CSA approved |
|
Applications |
Floating-roof tanks, pump cutoff, overfill alarms |
|
Chain / Hardware |
Stainless-steel beaded chain |
|
Calibration |
Factory set (custom chain lengths available) |
Have a look at the flyer to get all the tech specs and product features.
Brochure
Read the manual for detailed information and instructions.
Manual
Check out a sample cert from our calibration lab.
Certificate
If you have a question that we have not covered then just get in touch and we’ll be happy to help.
We have tried to answer the most common questions we are asked here.
Lead has high density, making it stable against wind and roof vibration — avoiding false alarms common in floating-roof tanks.
Yes — all mechanics are external, allowing safe maintenance without tank entry.
By mounting on the roof of the tank, all mechanical components and the electrical switch housing are located outside the product. This allows field technicians to perform routine inspection, functional testing, and maintenance of the switch without requiring any tank entry, degassing, or breaching the liquid level, dramatically improving safety and reducing service time.
No. The Omnitrol 721 is a dual-stage switch that operates from a single top-mounted penetration. It contains two separate switching mechanisms, both actuated by the same displacer chain assembly, allowing you to establish two independent alarm setpoints (Hi and Hi-Hi) with one device.
No — it operates using mechanical displacer movement and magnetic switching.
Yes — available in explosion-proof housings with UL/CSA approvals.
Floating-roof crude, refined product, and blend tanks at refineries, terminals, and tank farms.