Limit Switch for Pneumatic Actuator | IP67 | Mechanical 250V
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$81.00 USD
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Limit Switch for Pneumatic Actuator — IP67, Mechanical 250V, 1/2" Connection, as it confirms open and closed position of the actuator
The Cematic limit switch for pneumatic actuators detects and signals the actuator's position — fully open or fully closed — in standard industrial installations. Unlike positioners that control the actuator's position via a continuous signal, the limit switch only detects the two extreme states of travel: fully open and fully closed valve.
Upon reaching either of these positions, the mechanical switch signals the PLC that the actuator has reached its limit, as this is the data the system needs to continue the process sequence. Available in Small and Medium sizes to fit different actuator models.
Why the limit switch is different from the positioner — and when it is the correct specification
The limit switch and the positioner are two distinct accessories for pneumatic actuators. Confusion between the two is common, as both are mounted on the actuator and connected to the control system. However, their functions are completely different:
- Limit Switch — for ON-OFF systems where the PLC needs position confirmation, as without it the sequence cannot advance: In ON/OFF control systems, the PLC sends the open or close signal and awaits confirmation from the switch to proceed to the next stage of the sequence. Without this confirmation, the system does not know if the valve has reached the correct position.
Therefore, it may advance with the valve in the incorrect position or wait indefinitely. The limit switch provides this physical confirmation of the actuator's position.
- Positioner — for proportional control where continuous positioning is required, as the switch only detects the ends of the travel: The positioner regulates the actuator's position at any point between 0% and 100% opening. It is the correct accessory in PID control loops where the valve acts as the final control element. The limit switch, on the other hand, cannot perform this function as it only detects the two ends of the travel.
- Both accessories together — since they are often used simultaneously in many installations: In control valves with a positioner, it is common to also install a limit switch to confirm the ends of the travel. The positioner regulates the position during modulation. The switch also confirms when the valve reaches the ends of the travel.
IP67 and two sizes — why these features define the correct installation according to the actuator
IP67 protection and availability in two sizes are the main selection criteria for this switch. Their implications are described below, as they determine the correct installation:
- IP67 — protection against immersion at 1 meter for 30 minutes, since many actuators operate outdoors or with water cleaning: The IP67 rating ensures that the switch operates correctly even when exposed to pressurized water or heavy rain. It is the correct protection for actuators in outdoor installations or in plants where water cleaning is performed. Therefore, it is significantly more robust than a standard IP54 or IP65 switch.
- Small size — for compact actuators of smaller size, as the switch must match the actuator's footprint: The Small size ($1,293 MXN) is compatible with smaller diameter pneumatic actuators. It is the correct choice when mounting space on the actuator is limited. The Small size is also the lowest cost within the family.
- T4 — maximum surface temperature of 135°C, suitable for most industrial gases: Class T4 guarantees that the external temperature of the switch does not exceed 135°C under any operating conditions. The ambient operating temperature ranges from -25°C to 85°C, making it the correct specification for most industrial environments.
Technical specifications that define the installation limits of the explosion-proof limit switch
| Parameter | Value |
|---|---|
| Switch type | Mechanical |
| Function | Detection of open and closed actuator position |
| Available sizes | Small and Medium |
| Ex Certification | Not applicable — for non-hazardous areas |
| Enabled zone | Non-Ex classified zones — standard industrial installations |
| Maximum voltage | 250V AC/DC |
| Minimum voltage | 8V DC |
| Connection | 1/2" |
| Ambient temperature | -25 °C to +85 °C |
| Position indicator | Visual — 0° to 90° range |
| SKU | PASC01 and PASC02 |
Standard vs. Ex-Proof Limit Switch — comparative table to select the correct one based on the installation area
| Criterion | Standard IP67 Limit Switch ← This product | Ex-Proof Limit Switch (EXDIIBT4) |
|---|---|---|
| Main function | ✅ Confirms open or closed position — same as Ex-Proof but without zone certification | Regulates the actuator position at any point of travel |
| Compatible control type | ✅ ON-OFF — for any pneumatic actuator in a standard zone | Proportional — 0% to 100% opening |
| Signal to PLC | ✅ Digital — open or closed contact, also compatible with PLC | Analog 4-20 mA or digital depending on the model |
| Operating voltage | ✅ Up to 250V AC/DC — can switch loads directly from 8V | Control signal 4-20 mA — does not switch power loads |
| Ex Certification | IP67 — for installations without classified zones | Varies by model — verify positioner certification |
| Relative cost | ✅ Lower than Ex-Proof — justified when zone certification is not required | Higher — justified when proportional control is required |
| Joint installation | ✅ Compatible — can be installed with a positioner on the same actuator | Use Ex-Proof switch when the zone is classified |
Main applications of the explosion-proof limit switch where position confirmation is a requirement
- Position confirmation of pneumatic valves in ON-OFF control systems with a classified zone: In process sequences where the PLC needs to confirm that the valve has reached the correct position before continuing, the limit switch provides this confirmation directly and reliably. The IP67 also guarantees its operation in environments with water, steam, or dust typical of such installations.
- Petrochemical industry and refineries where shut-off valves operate in Zone 1 and Zone 2 areas: In refinery and petrochemical plant process units, line shut-off valves open and close in response to process conditions or emergency signals. The switch confirms the position to the control room.
Remote confirmation is, since the PLC cannot assume the valve has reached its destination, a process safety requirement.
- Gas distribution systems where incorrect valve position is a safety risk: In natural gas and LPG networks, the limit switch signals the SCADA system the position of each shut-off valve. Consequently, the operator can verify from the control room if all valves are in the correct position, especially during emergency maneuvers or maintenance.
Applications in industrial plants where position monitoring also improves safety and efficiency
- Continuous process plants where sequence automation requires position confirmation: In automatic start-up, shutdown, and filling sequences, the PLC advances from one stage to the next only when the switch confirms that the valve has reached the correct position. Without this confirmation, the system would wait indefinitely or advance with the valve in the incorrect position. Therefore, the limit switch is a standard component in this type of automation.
- Classified zones in the chemical industry, mining, and power generation where certified accessories are required: In any installation with Zone 1 or Zone 2 where position monitoring of pneumatic actuators is needed, this switch is the correct specification. The two available sizes also cover most pneumatic actuators in the Cematic catalog without the need for adapters.
For the complete range of actuator accessories, see pneumatic actuator accessories →