What is an oil pressure switch in a diesel generator? How does it work?

The simplest way to define a diesel generator oil pressure switch is as a diesel engine protection device. An oil pressure switch, as the name suggests, monitors the oil pressure of a diesel engine. This switch can usually be found on the engine block and can be found in either of two states – open or closed.

When the oil pressure is low, the switch can be found closed to ground when it fails. On the other hand, if the oil pressure is above the minimum requirement, the switch is in the open state.

The minimum oil pressure requirement at which a diesel engine should shut down is determined and set by the engine manufacturer to help prevent any problems or catastrophic failure of the diesel engine.

Did you know? Many times, it is the diesel engine manufacturer that provides the oil pressure switch.

Oil Pressure Switch – Application

In most cases, the oil pressure switch is used to ensure that the diesel engine is not running before starting. Here, the switch needs to be in the default state, which is grounded. The operator checks that the switch is in this resting position before starting the engine to avoid engaging the starter motor when the engine is already running, as this can cause a starter failure.

Again, the oil pressure sensor also doubles as an actuator. Here, once the oil pressure in the diesel engine falls below a preset critical level, it activates the oil warning light on the dashboard. This timely signal from the oil pressure gauge helps prevent any major damage to the engine.

While it may vary depending on the overall structure of the engine, the oil pressure sensor is usually located in a common area such as the engine's cylinder block or oil filter housing. In some cases, the oil pressure gauge can be located on the engine head.

How an Oil Pressure Switch Works

In most cases, the oil pressure sensor operates through a self-elastic diaphragm, also known as a movable diaphragm with a hairspring. The position of this diaphragm is a direct result of the pressure applied to it, which is why every diesel generator OEM assigns a different oil pressure threshold to each engine, usually in the range of 3.5 to 11psi.

When the oil pressure falls below the critical value, the oil pressure sensor activates a warning light or simply returns a signal to the ECU. This helps to alert the operator in time to prevent any damage to the engine.

In a switch with normally open contacts, the contacts are activated when the oil pressure in the engine reaches a specified critical level. This facilitates the movement of the diaphragm, causing the contacts to connect together, thus placing the switch in the closed position.

On the other hand, in switches with normally closed contacts, the contacts are deactivated when the oil pressure in the engine reaches a specified critical level. This facilitates the movement of the diaphragm, causing the contacts that were already connected to now disconnect together, thus placing the switch in the open position.

Like the critical oil pressure, the type, power and construction of the engine may also vary from manufacturer to manufacturer and the needs of the engine in question.

Diagnostic and testing procedures for oil pressure switches:

Case 1 – Switch with normally open contacts

In this case, it should be checked for an open circuit between the contacts when the engine is not running.

Next, it should be checked for a short circuit (continuity) between the contacts when the engine is running.

Finally, the continuity and condition of the pins, terminals and wires need to be checked.

Case 2 – Switch with normally closed contacts

In this case, it should be checked for a short circuit (continuity) between the contacts when the engine is not running.

Next, it should be noted for an open circuit between the contacts when the engine is running.

Finally, the continuity and condition of the pins, terminals and wires must be checked.

Testing the oil pressure switch with a multimeter

In order to test the oil pressure switch with a multimeter, the following steps must be followed:

First, unplug the connector from the oil pressure switch and check the connectivity between the contacts. If the switch comes with two pins, the check should be between the pins. If the switch has only one pin, the check should be between the pin and the mass (negative pole).

When the ignition switch is not turned on, the resistance reading of the multimeter should be infinite (contacts disconnected – closed) for switches with normally open contacts and zero (contacts connected – connected) for switches with normally closed contacts.

When the engine is running, the resistance reading of the multimeter should be zero (contacts connected – connected) for switches with normally open contacts and infinite (contacts disconnected – closed) for switches with normally closed contacts.

However, you should not be too worried about this aspect, especially if you purchase a diesel generator from Chongqing Kangbang, which will ensure that the diesel generator has been strictly inspected and tested to ensure that the diesel generator set is delivered and installed without any problems.

Common questions about oil pressure switches:

What is the procedure for checking the oil pressure switch?

One of the simplest ways to test the oil pressure switch is to connect a multimeter between the pins and the body of the sender. The switch should be closed when the engine is off and open when the engine is running.

What are some reasons for a drop in oil pressure?

A loss of engine oil supply is usually caused by oil viscosity that is too low or too high. Typically, when the viscosity is very high, it creates a high level of resistance during pumping of the oil. This causes a lack of lubrication within the system, ultimately resulting in a drop in pressure.

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