Skip to main content

Pressure Gauges

Pressure Gauges


Pressure gauges are connected to pipes to physically display the flow pressure - particularly the static pressure.


Why do we need to monitor pressure in the first place?


Pressure reading before and after equipment can indicate whether the component is running correctly or not.


A high pressure drop is usually a result of a clog or a leak somewhere.


To select a pressure gauge, two parameters are most important: accuracy and range.


The range of a pressure gauge is the maximum pressure reading possible on that gauge. It is a good practice to aim for a range that is 1.5-2 times the system's working pressure, with the maximum allowed pressure somewhere in the range. (relief valve pressure)

The accuracy of a pressure gauge is expressed by a +/-percentage of error in the pressure reading. For accuracy, ASME (American Society of Mechanical Engineers) has set standard classes for pressure gauges. Grades B, 1A & 2A.


In a typical chilled water system, Grade B gauges do the job for most locations. They have an accuracy of +/-3-2-3%, which means that at the beginning and end of the range, they have a 3% tolerance and a 2% in the middle.


It is recommended to place higher accuracy gauges, 2A for example, before and after pumps because they have an accuracy of +/- 0.5%. A few psi's difference in the pump's pressure can significantly change the flow rate of the system.


Where are pressure gauges located?


Before and after pumps, strainers, chillers, fan coil units, air handling units, micro bubble air and dirt separators, etc.


Types of pressure gauges:

  • Bourdon tube gauge: Most used in chilled water system. This type of pressure gauge features a simple design with high accuracy. Not suitable for viscous fluid applications.
  • Diaphragm gauge: Used in applications with high pressures and temperatures, as well as highly viscous fluid.
  • Bellows gauge: This type of gauge can measure the absolute, gauge and differential pressure.


Materials of pressure gauges:  

Stainless steel: which is highly resistant to corrosion, but not suitable for very high temperatures

Inconel: which is a nickel-chrome based superalloy. Most resistant to corrosion, even at high temperatures

Aluminium

Copper alloy


Note: Always check the compatibility of the working fluid with the material of the gauge.


Gauges are either air filled or oil filled.


Air filled gauges are less accurate and more susceptible to fluctuations due to vibration.


Oil filled gauges are more accurate. The oil damps vibration to provide a more stable reading. Oil filled gauges must be of high quality to make sure they do not leak.



Comments

Post a Comment

Popular posts from this blog

VALVES USED IN A CHILLER SYSTEM AND THE TYPICAL VALVE PACKAGE

  VALVES USED IN A CHILLER SYSTEM AND THE TYPICAL VALVE PACKAGE 1.Chilled Water Side Valves ⇒Isolation valve (manual/electric actuated). ⇒ Installed on CHW supply and return lines.  ⇒ Used to isolate chiller for maintenance. 2. Balancing Valve (Manual or Automatic)  ⇒ Ensures correct flow rate to/from chiller.  ⇒ Helps maintain Delta T and proper flow distribution.  ⇒ Located after evaporator outlet (return line). 3. Differential Pressure Bypass Valve (if 2-way valves in system)  ⇒ Prevents excess pressure build-up when terminals shut.  ⇒ Maintains flow through chiller. 4. Flow Switch  ⇒ Senses chilled water flow across evaporator.  ⇒ Safety interlock: trips chiller if flow is lost.  ⇒ Usually paddle type or electronic. 5. Air Vent Valve (Manual or Automatic)  ⇒ Removes air pockets.  ⇒ Placed at high points of piping and chiller headers. 6. Drain Valve  ⇒ For flushing, cleaning, and maintenance.  ⇒ Located at low poin...
Post a Comment
Read more

HVAC MEP Thumb Rules & Formulas (With Examples)

  HVAC MEP Thumb Rules & Formulas (With Examples) 1. Heat Load Calculation  Formula: Q = Area (sq.ft) x Heat Load Factor (BTU/hr per sq.ft) Example: 500 sq.ft office: Q = 500 x 30 = 15,000 BTU/hr TR = 1.25 2. CFM Calculation Formula: CFM = Sensible Heat (BTU/hr) / (1.08 x Delta T) Example: 12,000 BTU/hr, Delta T = 20°F CFM = 556 3. AHU/FCU Sizing Rule: 1 TR = 400 CFM 2 TR Airflow = 800 CFM 4. Duct Sizing Velocity Limits: Main: 1400-1800 FPM 800 CFM @ 1000 FPM 0.8 sq.ft 14"x10" 5. Chilled Water Flow Rate Formula: GPM = BTU/hr / (500 x Delta T) Example: 24,000 BTU/hr GPM = 4.8 6. Pipe Sizing 1" pipe: 8-12 GPM 2" pipe: 30-40 GPM 35 GPM Use 2" 7. Chiller Sizing Formula: TR = BTU/hr / 12,000 Example: 60,000 BTU/hr → 5 TR 8. Cooling Tower Sizing Rule: Heat Rejection = 1.25 x Load 10 TR → Tower = 12.5 TR 9. Pump Head Calculation Formula: Power (kW) = (Q x H x 9.81) / (Efficiency x 1000) Example: Q = 5 L/s, H = 20 m, Efficiency = 0.75 Power 1.31 kW 10. Fresh Air Re...
Post a Comment
Read more

Type of Heat Exchanger

 There are several types of heat exchangers used in HVAC systems, including: 1. Coil Type:     - Chilled water coils     - Hot water coils     - DX (direct expansion) coils     - Evaporator coils     - Condenser coils 2. Shell and Tube Type:     - U-tube heat exchangers     - Straight tube heat exchangers 3. Plate Type:     - Plate and frame heat exchangers     - Plate and shell heat exchangers 4. Finned Tube Type:     - Finned tube heat exchangers 5. Spiral Type:     - Spiral heat exchangers 6. Regenerative Type:     - Regenerative heat exchangers 7. Adiabatic Type:     - Adiabatic wheel heat exchangers 8. Run-Around Coil Type:     - Run-around coil heat exchangers These heat exchangers are used in various applications, including: - Air conditioning - Heating - Ventilation - Refrigeration - Heat recovery - Industrial processes Each type of hea...
2 comments
Read more