High-Temperature Float Switch Selection: 6 Checks
Selection Guide / 4 min read
Choose a high-temperature float switch by checking the liquid, temperature range, pressure, installation, electrical load and required switching action together. A 200°C headline is only a starting filter. The useful question is whether the complete switch arrangement fits your tank and operating conditions.
First, confirm that you need point-level detection
A float switch changes contact state when liquid reaches a switching point. It can provide a high- or low-level signal; it does not provide a continuous tank-level reading. If you need a level trend or percentage-full display, first assess a continuous measurement solution. Cynergy3 selection guidance
For continuous measurement, see our radar level transmitter selection guide. It addresses a different measurement task; it is not a product replacement recommendation.
Six checks before selecting a model
1. Liquid and specific gravity
Record the liquid composition and its specific gravity at operating temperature. Temperature-related density changes can shift switching behavior. Compare against the manufacturer’s minimum liquid SG, then check material compatibility and possible deposits. A float must remain free to move. Flowline manual, pages 6 and 10
2. Normal and peak temperature
Specify normal operation and possible temperature surges. Include hot cleaning cycles if the installed switch will experience them. Do not treat a maximum temperature as evidence of a permitted temporary overload. Flowline manual, page 10
3. Pressure at the operating temperature
List operating pressure and possible surges alongside temperature. Separate maximum-temperature and maximum-pressure entries do not establish a combined operating envelope. If that combination is not documented, obtain model-specific confirmation before accepting the selection. Flowline application limits
4. Mounting and access
Check vertical or horizontal mounting, internal or external fitting, thread, available space, cable route and connection type. A matching thread does not settle whether the switch can be installed or its float can travel freely. Record the actual tank opening and access arrangement. Cynergy3 selection guide, page 4
5. The load connected to the contact
Record voltage, current, switching power and whether the load is resistive, inductive or capacitive. Review all applicable limits, not just the largest number. A motor or relay coil needs its own load assessment; a resistive rating does not establish suitability. Cynergy3 selection guide, page 4
6. The required high- or low-level action
State the required response as a sentence: for example, “change the control input when liquid falls below this level.” Then identify the required contact state and switching points. Normally open or normally closed alone does not describe the complete control sequence. Cynergy3 switching guidance
Reading a specification: Flowline LV3X and LH35
Flowline lists a −40 to 200°C process range for this family. Its product page distinguishes LV3X vertical mounting within ±20° and minimum liquid SG 0.7 from LH35 horizontal mounting within ±20° and minimum SG 0.6. These are different installation and buoyancy requirements despite the shared temperature range. Flowline product specifications
For the vertical versions, LV35 uses a 1/8-inch NPT connection and LV36 a 1/4-inch NPT connection. Read the exact ordering code before comparing a tank connection. The linked data sheet is DS801839 Rev B, dated 2015; its presence on the current product page does not make it a new revision. Flowline data sheet
Reading a specification: Cynergy3 SSF26
The SSF26 is a vertical, internal-fitting switch rated up to 200°C, with minimum liquid SG 0.65. It installs from inside the tank at the top or bottom. A sealed tank without suitable internal access therefore presents an installation problem even if temperature and liquid SG appear suitable. Cynergy3 SSF26 product page
Its data sheet separates float SG 0.55 from minimum fluid SG 0.65: use 0.65 when screening the liquid. It also states that no sealing gasket is supplied. The connection and sealing arrangement therefore need review as part of the installation. SSF26 data sheet, page 1
Example: a liquid with SG 0.68
Suppose the liquid’s confirmed SG at operating temperature is 0.68. That is below the LV3X minimum of 0.7, so LV3X fails this initial screen. It exceeds SSF26’s 0.65 minimum, so SSF26 passes only the SG screen. Temperature, pressure, compatibility, access and load still require checks; this is not a replacement recommendation. Flowline · Cynergy3
Example: why 50 VA and 0.5 A are separate limits
The SSF26 data sheet gives maxima of 50 VA, 300 V AC/DC and 0.5 A, all for resistive loads. At 24 V, calculating 50 ÷ 24 gives about 2.08 A, but the separate 0.5 A limit still applies. At 230 V AC, a 0.5 A resistive load is 115 VA and exceeds 50 VA. Passing one line is insufficient. These calculations do not approve direct motor switching. SSF26 electrical ratings
Check the installed switching behavior
Keep the float away from severe turbulence or provide suitable protection. Verify the actual rising and falling actuation points in the application liquid and confirm the receiving controller responds as intended. Free movement and a correct contact signal both matter. Flowline manual, pages 3 and 10
Prepare a useful selection record
Bring together the six checks, the exact part code, a tank sketch, required approvals and the proposed electrical interface. Mark unresolved conditions explicitly before final selection. This makes the remaining questions specific enough to resolve against the manufacturer’s documentation. Cynergy3 selection guide
Official specifications
Related measurement guide
Radar level transmitter selection
Continuous level measurement is a different task from point-level switching.