How To Select a Manometer

Purpose of Manometer:

The manometer is a device used to measure the gas or liquid pressure against the atmospheric pressure. It is one of the most common methods used to measure absolute pressure. Being a pressure-sensitive device, it is frequently used in

  • Detecting leakage in tubing and casing
  • Static mud columns for gradient
  • Fluid inflow in any perforation measurements
  • Physiological measurements, such as blood pressure
  • Weather conditions and meteorological measurements.
  • Engineering applications, such as bridge construction and installing swimming pools.

Types of Manometer:

There are two types of manometers:

  1. Analog meters
  2. Digital meters

 

Analog and Digital meters

Analog meters, also known as dial gauges, are U-shaped containers using hydrostatic balance to make measurements. They have a needle that points directly at the values in the scale with respect to the pressure sensed by the measuring element. Digital meters are developed with a sensing element, also known as pressure transducers, that can convert the sensed pressure into an electric signal and display the readings on a digital meter. Since they are portable with more advanced features, they are preferred over analog meters.

 

Reasons to choose Digital Meters

  • Calibration
  • Customization
  • Flexibility
  • Readability
  • Accuracy
  • Durability

 

Selection Factors

 PRESSURE RANGE:

The primary factor to be considered in selecting a Manometer is its operating range. Under normal conditions, it must be ensured that the pressure does not exceed 25%-75% of the total readings on the scale. On the other hand, if pulsation is present, then the gauge’s pressure must not exceed 50% of the total readings on the scale.

ACCURACY:

It is common for devices to differ in the accuracy levels depending upon the manufacturer. The acceptable range of accuracy falls anywhere between ±.25 and ±2.5 percent depending on the manufacturer. This factor also depends upon the type of scale used, single or dual range. For any mechanical gauge, the percentage of the full-scale range is considered as accuracy. The general guidelines for the accuracy level on a full-scale range for the different processes are as follows:

Critical process – 0.5%

Standards and test gauges – 0.10% – 0.25%

Less commercial process – 2%

General industrial process – 1%

Sometimes overpressure, external temperature, vibrations can result in lower system accuracy.

SIZE OF DIAL:

The dial size usually depends upon the application, available space, and the readability requirements. Generally, it varies from ½ inch (1.27cm) to 16 inches (40.64cm) in diameter, where the measurement involving 0.25% to 0.5% accuracy is 4 1/2 inches (11.43cm) in diameter.

 

PARTS USED: 

Since the device has both dry and wet parts, it is crucial to look for the types of materials used in production to avoid corrosion and ensure the product last longer. Some materials become harmful when mixed with other materials, this might result in gauge failure or corrosion. Therefore, it is essential to take care of the three vital factors while designing manometers.

  1. Chemical compatibility
  2. Corrosion
  3. Partial fatigue

If the wet components of the gauge are not compatible with the process, a diaphragm could be introduced.

 

MATERIAL SELECTION:

When selecting the type of material environmental conditions, such as ambient temperature, humidity, water, airborne particulates, and chemicals play a vital role. These factors could affect the overall performance of the pressure gauge by reducing accuracy and integrity. It is often preferred to select hermetically sealed or weatherproof designs to protect the Manometer from external ambient conditions that may be corrosive, humid, or contain large particulate matter. The pressure gauges are available as both temperature and non-temperature compensated for isolating it from the external conditions. The materials that are used for making a gauge case involve stainless steel 304 & 316L, carbon steel, ABS, and thermoplastics.

 

CONNECTION PARAMETERS:

The connection parameters include the connection location and the type used. The connection location includes the different mounting options that are to be considered, such as:

  • Well or surface mount with lower connect
  • Stem mount with lower connect
  • Panel mount with back connect
  • U-clamp flush mount with the back connect for panel mounting

With regards to the connection type, gauges are available with different configurations like SAE, DIN, NPT, JIS, and BSP. Among these, the best connection support is provided by the NPT.

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