Simple Sight Glasses and Gauging Rod level indicators

Simple sight Glasses:

A visual indication of the level can be obtained when part of the container is constructed with transparent material or the liquid in a container is dripped through a transparent tube. The advantage of using shutoff valves with the use of a bypass tube is the ease of removal for cleaning.

Simple sight glasses are an older technology and are very seldom used for automatic control applications. These are not highly suited for industrial applications as manual viewing and transmission of information is required by the operator.

Applications of such level measuring devices can be seen in tanks for the storage of lubricating oils or water. They provide a very simple means of accessing level information and can simplify the task of physically viewing or dipping a tank.

Sight glasses are also not suitable for dark or dirty liquids. This type should not be used when measuring hazardous liquids as the glass-tube is easily damaged or broken.


  • Very simple
  • Inexpensive


  • Not suitable for automated control.
  • Maintenance - requires cleaning
  • Fragile - easily damaged

Gauging Rod Method:

This requires a little more manual effort than the peephole, but it is another very simple and inexpensive method of accounting for the level. This method can be applied to liquids and bulk materials, and heavy steel belts can be used in very high silos. Service stations use this method to “submerge” their tanks, which use a notched immersion rod. A common example is the dipstick oil level in a motor vehicle.

This method is designed primarily for atmospheric conditions. The sliding tubes can be used for pressure vessels, but require the ventilation of the gas or process liquid in the atmosphere. These devices are hazardous to personnel and should not be used in designated safe areas or for control as part of an automated process.


  • Simple and inexpensive.


  • Sampled measurement only
  • Hazards associated with pressurised measurement
  • Limited accuracy