Why it matters: Understanding the difference between pneumatic-to-electric and electric-to-pneumatic devices is crucial for technicians.
- The blog provides simple explanations and memory aids for each device.
- Practical examples and troubleshooting tips to assist technicians.
- Comparison charts and direct links to shop PE and EP switches.
- Learn how to identify the right device for BAS or pneumatic retrofit projects.
- Know where to find replacement products or support easily.
What Is a PE or EP Switch in an HVAC Pneumatic Control System?
PE and EP devices help bridge the gap between older pneumatic control systems and modern building automation systems. Here is what they do, how they work, and how to remember the difference in the field.
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Why PE and EP Devices Matter
Even though modern building automation systems are increasingly digital, pneumatic controls are still found in thousands of commercial buildings across North America. Schools, hospitals, government facilities, and older office buildings often continue to rely on pneumatic actuators, thermostats, and control devices that have been operating reliably for decades.
As these systems are upgraded or integrated with modern Building Automation Systems, technicians frequently encounter devices labeled PE or EP. Understanding what these devices do is essential when troubleshooting control problems, retrofitting older systems, or connecting pneumatic equipment to digital controls.
Simple way to think about it: PE and EP devices are translators between two control worlds. One converts electrical signals into pneumatic pressure, while the other converts pneumatic pressure into electrical signals.
Easy Memory Trick
EP = Electric ? Pneumatic
The controller tells the air system what to do.
PE = Pneumatic ? Electric
The air system tells the controller what is happening.
EP Transducer: Electro-Pneumatic
An EP device converts an electrical control signal from a BAS or DDC controller into a pneumatic pressure signal. This allows a modern controller to operate older pneumatic valves, dampers, and actuators.
Common Inputs
- 0–10 VDC
- 2–10 VDC
- 4–20 mA
Common Outputs
- 3–15 PSI, most common
- Other pneumatic ranges possible
Example
A DDC controller may send a 4–20 mA signal to control a pneumatic valve. The EP transducer converts that electrical signal into a proportional 3–15 PSI pneumatic signal.
| Electrical Input | Pneumatic Output | Typical Result |
|---|---|---|
| 4 mA | 3 PSI | Valve closed |
| 12 mA | 9 PSI | Mid-position |
| 20 mA | 15 PSI | Valve open |
Where You’ll Find EP Devices
- Near control valves
- On pneumatic damper actuators
- In mixed DDC and pneumatic retrofit systems
- Mounted inside control panels
PE Transducer: Pneumatic-Electric
A PE device converts a pneumatic pressure signal into an electrical signal that a BAS controller can read. This allows the BAS to monitor what is happening in a pneumatic system.
Common Inputs
- 3–15 PSI pneumatic signal
Common Outputs
- Dry contact
- 0–10 VDC
- 4–20 mA
- Digital input status
Example
If a pneumatic signal is controlling a valve, a BAS may need to trend valve position. A PE transducer can convert a 3–15 PSI signal into a 4–20 mA signal that the BAS can monitor.
| Pneumatic Input | Electrical Output | Typical BAS Reading |
|---|---|---|
| 3 PSI | 4 mA | 0% |
| 9 PSI | 12 mA | 50% |
| 15 PSI | 20 mA | 100% |
Where You’ll Find PE Devices
- Pneumatic monitoring applications
- Alarm circuits
- Pneumatic system retrofits
- Interface panels between BAS and pneumatic controls
What Is a PE Switch?
A PE switch is slightly different from a PE transducer. A switch is typically an on/off device rather than a proportional signal device.
Example: If the setpoint is 8 PSI, pressure below 8 PSI may leave the contact open, while pressure above 8 PSI may close the contact.
A PE switch does not tell the BAS the exact pressure. It simply indicates whether pressure is above or below a setpoint.
Common Uses
- Compressor status
- Main air pressure alarms
- Safety interlocks
- Low air pressure alarms
What Is an EP Switch?
An EP switch is less common than an EP transducer. Instead of producing a proportional pressure signal, it uses an electrical signal to switch pneumatic air on or off.
Think of it like an electrical relay for air pressure. When energized, air may pass through. When de-energized, air may be blocked or exhausted.
You May Also Hear These Called
- Solenoid air valves
- Pneumatic relays
- Air switching valves
Quick Comparison Chart
| Device | Input | Output | Primary Purpose |
|---|---|---|---|
| EP Transducer | Electrical | Pneumatic | Control pneumatic devices from BAS |
| PE Transducer | Pneumatic | Electrical | Monitor pneumatic signals in BAS |
| PE Switch | Pneumatic | Electrical Contact | Alarm or status indication |
| EP Switch | Electrical | Air On/Off | Switch air flow using electricity |
Easy Field Troubleshooting Rule
When troubleshooting PE and EP devices, start by identifying which direction the signal is supposed to travel. That will quickly tell you what side of the device to check first.
Electric ? Pneumatic
Ask: Is the BAS sending the correct voltage or current? If yes, check whether the EP is producing the correct PSI output.
Pneumatic ? Electric
Ask: Is the pneumatic pressure correct? If yes, check whether the PE is producing the correct electrical signal back to the BAS.
Looking for PE or EP Switches?
Stromquist offers PE and EP switches for pneumatic control systems, BAS retrofits, pressure monitoring applications, and HVAC control integration projects.
PE Switches
Convert pneumatic pressure into an electrical signal for alarms, status monitoring, and BAS integration.
EP Switches
Convert electrical signals into pneumatic action for pneumatic valves, dampers, and BAS retrofit applications.
Need Help Identifying a PE or EP Device?
Whether you are troubleshooting a pneumatic control issue, retrofitting an older building, or integrating pneumatic equipment into a modern BAS system, Stromquist can help you find the right solution.