Direct Answer
If the customer only needs the pump to start and stop at preset pressure points, a pressure switch can be used.
If the customer needs constant pressure water supply, VFD control, PLC control or automatic pump speed adjustment, a pressure transmitter should be selected.
A pressure switch provides an on/off signal when pressure reaches a setpoint, while a pressure transmitter provides continuous pressure feedback. Constant pressure water supply requires real-time pressure feedback so the VFD or PLC can adjust pump speed continuously.
Pressure Switch: Best for On/Off and Protection
A pressure switch is suitable for pump start/stop control, high pressure alarm, low pressure protection, dry-run protection and safety interlock.
Best for:
- simple pump start/stop control;
- high pressure shutdown;
- low pressure alarm;
- compressor pressure control;
- filter blockage alarm;
- pump protection interlock.
The limitation is that a pressure switch does not provide the actual pressure value. It only tells the control system whether pressure has crossed a setpoint.
Pressure Transmitter: Best for Constant Pressure Control
A pressure transmitter converts pressure into a continuous signal such as 4–20mA or 0–10V. This signal can be sent to a PLC, VFD, HMI or control panel.
Best for:
- constant pressure water supply;
- booster pump systems;
- VFD pump control;
- PLC pressure feedback;
- water treatment pump skids;
- remote pressure monitoring.
In constant pressure VFD systems, the controller reads the pressure feedback and adjusts motor frequency to maintain the target pressure.
Why a Pressure Switch Alone Is Not Enough for Constant Pressure
A pressure switch can start the pump at low pressure and stop it at high pressure. This creates a pressure range, not true constant pressure.
For example:
- start below 3 bar;
- stop above 5 bar.
The system pressure still fluctuates between 3 and 5 bar. The pump can only start or stop; it cannot adjust speed smoothly.
A pressure transmitter allows the VFD or PLC to compare actual pressure with the target pressure and adjust pump speed continuously. This is why transmitters are the better choice for constant pressure systems.
NC20 Mechanical Pressure Controller
Best Practice: Use Both
For a reliable constant pressure system:
Use a pressure transmitter for control, and use a pressure switch for protection.
| Function | Recommended Device | Purpose |
|---|---|---|
| Constant pressure control | Pressure transmitter | Continuous feedback to PLC/VFD |
| High pressure protection | Pressure switch | Alarm or shutdown |
| Low pressure protection | Pressure switch | Dry-run protection |
| Local pressure display | Digital pressure gauge | Field inspection |
| Remote monitoring | Pressure transmitter | Trend and data output |
NOIKE-AH Application Solution
For constant pressure water supply, NOIKE-AH NT30D Pressure Transmitter can provide continuous pressure feedback to PLC, VFD or control panel.
For protection, NOIKE-AH NT30B Intelligent Pressure Switch can be used for high pressure shutdown, low pressure alarm, dry-run protection and pump interlock.
For local inspection, a Digital Pressure Gauge can help technicians compare actual pressure with PLC/VFD display and transmitter output.
NOIKE-AH Pressure Series includes pressure transmitters, pressure switches, pressure sensors and pressure gauges for industrial pressure monitoring and control applications.
Selection Guide
| Customer Requirement | Recommended Device | Reason |
|---|---|---|
| Simple pump start/stop | Pressure switch | On/off control is enough |
| High/low pressure alarm | Pressure switch | Setpoint-based output |
| Constant pressure supply | Pressure transmitter | Continuous feedback required |
| VFD speed control | Pressure transmitter | VFD needs analog pressure signal |
| PLC pressure trend monitoring | Pressure transmitter | Real-time pressure data |
| Dry-run or overpressure protection | Pressure switch | Safety interlock |
| Local reading | Digital pressure gauge | Field verification |
Conclusion
For constant pressure water supply, the main control device should be a pressure transmitter, because the VFD or PLC needs continuous pressure feedback. A pressure switch should be used as a protection device for high pressure alarm, low pressure alarm, dry-run protection and safety interlock.
NOIKE-AH recommends using NT30D Pressure Transmitter for pressure feedback, NT30B Intelligent Pressure Switch for protection, and a Digital Pressure Gauge for local pressure verification. This combination supports stable water pressure, automatic speed control, alarm protection and easier field maintenance.
