Underground tanks refer to tanks installed below the ground for storing gas or liquid. So is measuring the level of an underground tank the same as measuring the level of a tank above ground? The answer is no. Most underground tanks come pre-assembled. Once installed, it will not change year after year. The most common ones are underground oil storage tanks at gas stations.

So how to measure the liquid level of underground tanks? What tank level indicators are available? Let’s take a look together.

Underground Tanks

Underground tanks are generally installed pre-buried. After installation, it is difficult to make changes to the bottom, sides, etc. of the tank. Of course, underground tanks generally have reserved manholes, feed openings, discharge openings, etc. Some will also reserve installation locations specifically for level meters.

Based on our experience, underground tank level indicators can be divided into two categories: contact and non-contact. For example, ultrasonic level meter and radar level meter are commonly used non-contact level indicators. For example, Hydrostatic Level Sensor, float level sensor, and magnetostrictive level meter are commonly used contact level indicators.

The specific choice needs to be determined based on the conditions of the medium in the storage tank. The second half of our blog will explain this with examples.

Below are the various underground tank level indicators we supply at Sino-Inst. You can choose to delve deeper into the measurement parameters:

Available underground tanks level indicators

OK Next, we will use our actual cases to hand over the choice of underground tank level indicators for you.

Gas station underground oil storage tanks

We all know that most diesel and gasoline at gas stations are stored in underground tanks. The oil level needs to be accurately monitored in real time. Including when feeding and discharging materials. The accuracy of this tank level indicator needs to be very high. Because it is directly linked to money.

Gas station underground oil storage tanks

So based on our experience, in this case we would recommend users to choose Magnetostrictive liquid level sensor.

Mainly because Magnetostrictive liquid level sensor can meet the following characteristics:

  1. Large range: 0.2m~25m;
  2. Meet the explosion-proof requirements of gas stations. Explosion-proof level: ExdⅡCT6 Gb;
  3. High precision. Magnetostrictive level transmitter has a maximum accuracy of 1mm;
  4. Can meet high temperature, high pressure and other parameter customization. -40 ℃ ~ +350 ℃, 10MPa;
  5. The installation size can be customized. According to the installation requirements of underground oil storage tanks, threaded or flange installation can be configured.
  6. Support signal output, 4~20mA, 0~5V, 0~10V, HART, RS-485. It is convenient for real-time monitoring of oil level in the office.
  7. The Magnetostrictive level transmitter can also be customized according to needs: interface output (measurement of oil-water interface), and simultaneous output of temperature and liquid level (up to 8 RTD temperature sensors can be installed for temperature detection).

Read more about: Magnetostrictive Level Transmitter Working Principle

Of course, if the measurement accuracy requirements are not high. Then it is also possible to choose explosion-proof ultrasonic level meter.

Underground sewage storage tanks

Here is an example of a measurement taken by one of our users. Their 2 storage tanks are underground tanks for sewage.

  1. The 2 storage tanks are sewer septic tanks;
  2. The on-site storage tanks are underground storage tanks; horizontal tanks; the heights are 1800mm and 1500mm respectively;
  3. The tank has a reserved manhole of Φ450mm.

Comprehensive consideration of measurement parameters and installation dimensions. We configure anti-corrosion antennas for the optional 80G radar level meter. Customized installation dimensions for reserved manhole installation in the tank.

Read more about: Crude Oil Measurement, 80G Radar Level Meter Should Be Your First Choice!

Chemical corrosive raw material storage tanks

The capacity of underground storage tanks in the chemical industry can range from thousands to millions of gallons. For example, some large chemical plants may have underground storage tanks with a capacity of 300,000 gallons for storing raw materials such as ethylene and benzene.

This type of Underground Tanks level measurement will be more complicated than the above two. We need to comprehensively consider many factors, especially the characteristics of the medium:

  1. The size and shape of the tank.
  2. The temperature, pressure, viscosity, corrosiveness, etc. of the medium.
  3. Is there stirring in the tank?
  4. The installation position of the inlet and outlet, etc.;

Here we discuss the level indicators available for corrosive media. Generally there are radar level meters and guided wave radar level meters. Or customize an anti-corrosion input level sensor made of PTFE.

The following is also a case of measurement by one of our customers. The measuring medium is: a metal tank containing 98% sulfuric acid. The tank is large and comes with a picture of the level transmitter installed.

We equipped him with an antenna made of PTFE anti-corrosion material to meet the measurement requirements:

Radar level meter
Model: FMW11
Measuring the level in a sulfuric acid tank
PTFE antenna,
Temperature resistance: -40-80℃,
Pressure: -0.1-0.3MPa
Mounting Dimensions: 1 1/2″ NPT PTFE Coated
Digital display with measurement and programming
4-20mA (two wires) +HART
1/2″ NPT Head Electrical Connections


To check the water level in your underground tank, there are several methods you can use:

  • Manual measurement: Use a dipstick or water measuring rope to lower it into the water tank to directly measure the water level.
  • Install a water level sensor: Install a float or pressure water level sensor in the water tank, which can monitor the water level in real time.
  • Electronic water level indicator: uses an electronic probe to monitor the water level and displays the water level height through a digital display.
  • Ultrasonic water level meter: Ultrasonic waves are emitted from the top of the water tank and the water level height is calculated based on its reflection time.
  • Radar water level gauge: Using the principle of radar waves, the signal is also emitted from the top of the water tank and the reflection time is measured to determine the water level height.

The best water level indicator depends on the specific application scenario and needs, such as accuracy requirements, installation environment, maintenance costs and budget. The more commonly used ones at present are:

  • Ultrasonic water level meter: non-contact measurement, less maintenance, suitable for most application scenarios.
  • Radar water level gauge: It is also non-contact and suitable for extreme working conditions, such as high temperature, high pressure, corrosive media and other environments.
  • Float water level switch: simple and reliable, low cost, but average accuracy.
  • Capacitive water level sensor: high accuracy, but relatively complex to install and expensive.

The main difference between a water level indicator and a water level gauge is their function and usage:

Water level indicator (Level Indicator) usually refers to a visual or electronic display of the water level inside the container. It can be a simple window or a complex electronic device that converts water level information into readable data.

Water level gauge (Level Gauge) refers more to a measuring tool or device, which is used to accurately measure and read water level. Water level gauges often provide more detailed water level data, such as precise readings in millimeters or inches.

Simply put, water level indicators tend to visually display water level status, while water level gauges provide more precise measurements. In actual industrial applications, the water level indicator may be part of the water level gauge for visual display, while the water level gauge is part of the entire measurement system.

More Level Measurement Solutions

An important reason for using underground storage tanks is that they can reduce the occupation of surface space. At the same time, they have certain functions of thermal insulation, fire prevention and reducing environmental pollution. However, underground storage tanks also require strict compliance with environmental regulations and safety standards to prevent leaks and contamination of soil and groundwater. Liquid level monitoring of underground storage tanks can effectively avoid economic losses.

We at Sino-Inst are professional suppliers of Underground Tanks level indicators. We provide users with various standard and customized level meters. It can meet the liquid level measurement needs of various tanks with different parameters.

If you need to measure Underground Tanks level, please feel free to contact our sales engineers for consultation.

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