Level Switches – Always Keep an Eye on Your Oil Tank

Hydraulic systems must always store sufficient oil. Therefore, permanent monitoring of the oil level is essential. If a hydraulic pump runs dry, it can be damaged. The failure of a hydraulic system can cause significant damage to the entire plant. To prevent this, level switches and level sensors are installed to monitor the oil level in the hydraulic tank.

Level Switches Help with Leaking Hydraulic Oil

Hydraulic systems operate under very high pressure. Several hundred bar are quite normal for power transmission through liquids. While this is usually not an issue for steel pipes and hydraulic cylinders, it can lead to problems with connection pieces sooner or later. Especially seals, which become brittle and harden over time, may eventually no longer withstand the internal pressure of the hydraulic system.

However, the leakage of hydraulic oil is not always immediately noticed. Leaks can be deeply hidden within the system’s components. Therefore, the hydraulic oil level is ideally monitored directly at the tank. The level switch is a suitable tool for this purpose.

Three Ways to Monitor Fill Levels Using Level Switches

A level switch in a hydraulic tank usually consists of a float and an electrical assembly. In the simplest case, the float triggers a circuit breaker contact as soon as the hydraulic oil in the tank falls below its minimum level.

Float switches with an attached potentiometer are technically more complex. These units continuously transmit an actual value signal regarding the fill level, which is either monitored by a control unit or visualized on a display.

If only visual monitoring of the fill level is required, simple sight glasses or manual fittings are sufficient in many cases – especially in hydraulic applications.

However, a level switch is usually more than just a simple indicator: a switch closes or opens an electrical circuit. This signal change can be used for many applications.

Level Switches: Sensors, Switches, and Indicators

Several components are required to monitor a hydraulic oil tank. A typical minimum setup includes:

• Sensors provide an actual value of the oil tank’s fill level, either directly or indirectly. In the simplest case, these are floats connected to a rod that float on the oil’s surface in the tank. The higher the tank is filled, the higher the float and its connected rod rise. Indicators can then be attached to the rod.
• Indicators provide information about the tank’s fill status via a visual interface. These can be sight glasses, gauges, or electronic signals transmitted to a screen or a simple warning light. In hydraulics, oil systems are usually redundantly equipped with indicators: a direct, optical display is the minimum standard, while additional sensory transmission to an electronic interface is optional. Due to the complexity of modern hydraulic systems, electronic monitoring with corresponding output via digital indicators has now become standard.
• Switches, especially level switches, are the complement to sensors and indicators. Instead of passively showing the operator the actual status in the oil tank via indicators, level switches automatically trigger an action. The nature of this action depends entirely on the designers: the switching signal can be used to trigger a warning as well as for an emergency stop of the entire system.
  
  In addition to simple float switches, there are also level switches that operate with ultrasound or laser light. Ultrasonic level switches continuously emit a high-frequency sound signal that is reflected by the surface of the hydraulic oil. A receiver measures the time taken for the signal from emission to reception and calculates the tank’s fill level from this. This non-contact measurement method is very reliable and durable due to the absence of technical components. Besides ultrasonic sensors, laser measurement methods are also used for level measurement. These are also very reliable and can be calibrated for virtually any medium in any aggregate state.

Useful Additions to Level Switches

In addition to the fill level of a hydraulic tank, it is useful to sensorically monitor the content for other properties. Many hydraulic fluids used, for example, are highly hygroscopic. This includes even normal brake fluid, as used in vehicles. Hydraulic oil contaminated with water can lose many of its properties or significantly degrade them. It also contributes to the growth of fungi, which is a major problem in hydraulic systems. This danger can be professionally addressed with the help of suitable sensors.

Two Level Switches Are Better Than One

With any electronic system, one must always anticipate errors in the signal line. Few things are more sensitive than exposed cables: from corrosion at contact points to rodent bites, the wiring in a system can be damaged faster than any other component. For this reason, it is advisable to always install more than one level switch in a hydraulic tank. With a redundant arrangement, the control electronics always have a comparative value against which an actual state can be checked. An additional, purely manual-optical display ensures maximum safety.