Irrigation Pump Pressure Override – Preventing False Shutdowns During Engine Start
Many irrigation pump systems use a pressure switch to protect the engine and pump. If pump pressure is lost, the system shuts the engine down automatically.
During engine start-up the pump pressure is often low for a few seconds. This can cause the protection system to shut the engine down even though nothing is actually wrong.
The Problem
When a diesel irrigation engine starts, the pump needs a short time to prime and build normal pressure.
If the pressure protection system becomes active immediately, the engine may shut down before the pump pressure stabilises.
Typical field situation:
- Farmer starts the irrigation engine
- Engine runs normally for a few seconds
- Pump pressure has not yet built up
- Protection system detects “low pressure”
- Engine shuts down
Why This Happens
The pump pressure switch is not faulty. It is actually doing its job correctly.
The real issue is that the protection system becomes active before the pump pressure has had time to stabilise.
The Solution – Pressure Override Delay
To solve this problem, irrigation systems often use a temporary pressure override delay.
This delay temporarily bypasses the pump pressure sensor during engine start. Once the pump reaches normal pressure, the protection system becomes active again.
Simple idea:
- Engine starts
- Pressure sensor is temporarily ignored
- Pump builds pressure
- Protection system becomes active again
Using the BEM502IRN Protection Panel
The BEM502IRN irrigation engine protection panel already includes a built-in start delay.
During engine start the panel temporarily bypasses the protection sensors. This allows the engine and pump to stabilise before the monitoring system becomes active.
During this delay the output relay is energised and the front panel LEDs flash while the timer is running. Once the delay finishes, normal protection monitoring begins.
Extending the Override Time
Some irrigation systems require a longer override delay.
This can happen when:
- The pump is large
- The suction line is long
- The pump takes longer to prime
In these cases an additional timer can be installed in the control circuit.
Common timer solutions:
- BMT-55 mechanical timer – simple wind-up override timer BMT-55 4hours mechanical timer
- TM301 electronic timer module – adjustable delay timer Bolec TM301
Example Start-Up Sequence
- Operator starts the irrigation engine
- Override timer becomes active
- Pump begins building pressure
- Override delay expires
- Pump pressure protection becomes active
- System continues normal irrigation operation
Benefits of Using an Override Timer
- Prevents nuisance shutdowns during engine start
- Allows pump pressure to stabilise
- Maintains full engine protection once running
- Improves reliability of irrigation systems
A pump pressure override delay is a simple but important feature in many irrigation systems. It prevents false shutdowns during engine start while still maintaining full protection once the system is running normally.