Every float switch order starts with a conversation. Most customers know they need a level sensor, but the right configuration depends on details that aren’t obvious from a product page. The five questions below are the same ones our application engineers walk through on every call. Have answers ready and the spec process usually wraps in one conversation rather than three.

1. What Are the Dimensions of Your Tank?

Tank geometry drives nearly every other decision. Height determines stem length on a vertical float switch. Interior diameter or width determines whether the float has clearance to move freely without contacting the wall. Internal hardware (baffles, agitators, heating coils, fill pipes, sparge tubes) further restricts where a float switch can physically be mounted.

Dead band is one of the most overlooked dimensional issues. A narrow tank limits the vertical distance available between high and low set points on a multi-level switch, which in turn limits how much liquid you can store between pump cycles. Tank shape matters too. Conical or hopper-bottom tanks change how the lower set point behaves as level approaches the floor. Agitated tanks introduce turbulence that can cause a float to chatter against the switch contact, which is usually solved with a stilling well or a damped float design.

If the tank is already in service or hard to measure directly, a drawing works. So does a quick set of photos with a tape measure for reference.

2. What’s in the Tank?

Liquid chemistry drives material selection across the wetted parts: float, stem, seals, and any threaded fittings. Water, condensate, and most aqueous solutions are straightforward. Polypropylene or 304 stainless covers the majority of those applications. Chlorides change the calculus quickly, since 304 will pit over time even at low concentrations, so saltwater and chlorinated process water push the spec to 316 stainless. Acids, hydrocarbons, and solvents each push it further toward PVDF, PTFE, or specialty plastics. Seal selection matters as much as the wetted metal, since Buna-N, Viton, and EPDM each have different chemical resistance profiles, and seals often fail before the structural components do.

Beyond chemistry, four other liquid properties affect the spec. Specific gravity determines float selection, since a float sized for water won’t behave the same in a low-density solvent or a high-density brine. Viscosity affects response time and can interfere with reed switch actuation if the float can’t move freely. Particulates and suspended solids can foul a stem or coat a float, eventually changing its buoyancy. Foaming liquids can give a float false readings if the foam is dense enough to lift it.

If the liquid is a proprietary blend, an SDS or compatibility chart from the chemical supplier saves a lot of back and forth.

3. Are You Filling or Draining?

The application direction determines switch logic. A switch controlling a fill operation typically uses a normally closed contact that opens at the high set point to stop the pump or close the valve. A switch controlling a drain typically uses a normally open contact that closes at the high set point to start the pump or open the valve. Reversing the logic is the most common spec mistake we catch on the phone.

Whether you’re driving a pump or a valve also affects the electrical spec. Pump motors draw inrush current several times higher than their running current at startup, so the switch contacts need to be rated for that load or wired through a relay or contactor. Solenoid valves have their own inrush characteristics. AC and DC loads behave differently at the contact, with DC arcing more aggressively and shortening contact life if the rating isn’t matched. For higher-amperage loads, most installations use the float switch as a low-current pilot device that triggers a relay handling the actual motor or valve power. That separation protects the switch and simplifies replacement.

4. Where Should the Switch Trigger?

From the top of the tank down, where do you want the pump to start, and where do you want it to stop? The same logic applies to valves. Those two distances are your set points, and they determine stem length on a vertical switch and exact mounting elevation on a side-mount unit.

Set point spacing matters as much as the set points themselves. The distance between start and stop creates the operating dead band, which controls how often the pump cycles. Too tight a dead band and the pump short-cycles, which shortens motor life and stresses the contact. Too wide and the tank either overflows or runs dry depending on direction. For multi-level control with two or more floats on a single stem, there’s also a minimum spacing between floats to prevent magnetic interference between adjacent reed switches. That minimum varies by float diameter and stem design, and it’s usually the limiting factor on how tightly you can space your levels.

Accuracy expectations belong here too. Float switches are point-level devices, not continuous level sensors, and tolerance on the actual trigger point is typically a fraction of an inch around the nominal set point.

5. How Will the Switch Mount?

Top-mount switches install through a threaded fitting or flange on the tank lid. Side-mount switches thread through the tank wall at a fixed height. The choice depends on tank access, available openings, the kind of level control needed, and whether the tank is pressurized.

Thread spec is the detail that catches people most often. NPT and BSPT look similar but don’t seal against each other. Sanitary applications usually require tri-clamp fittings rather than threads. Pressurized tanks need flange ratings matched to the operating pressure, and any flange gasket has to be compatible with both the liquid and the temperature. Material of the fitting should match the wetted material of the switch where possible to avoid galvanic issues over time.

Insertion depth on a side-mount also matters. The float needs enough clearance from the inside wall to swing freely, and on a horizontal tilt switch, the swing arc has to be unobstructed.

Have Those Five Answers Ready

With tank dimensions, liquid type, application direction, set points, and mount style nailed down, our team can spec a switch on the same call. LiquidLevel manufactures custom float switches in Connecticut with no minimum order requirements, flexible pricing, and rapid turnaround. Call us or request a quote to talk through your application.