The Critical Role of Pressure Gauges in Aviation Fuelling

In the aviation industry, the safety and efficiency of fueling operations are paramount. One of the most crucial components in ensuring these standards is the Role of Pressure Gauges in Aviation Fuelling.

These instruments, along with pressure transducers, not only monitor fuel pressure but also play a vital role in preventing accidents and ensuring the integrity of fueling systems. This article delves into the importance of pressure gauges in aviation fueling, exploring their functions, types, maintenance, and the regulations governing their use.

Understanding Pressure Gauges in Aviation Fuelling

Pressure gauges are devices used to measure the pressure of gases or liquids within a system. In aviation fueling, they are essential for monitoring the pressure of fuel as it flows from storage/refueller tanks to aircraft. The accuracy and reliability of these gauges are critical, as they help prevent over-pressurization, which can lead to catastrophic failures. Proper maintenance of these gauges is crucial for leak detection and ensuring the integrity of the aviation fuel circuit.

Jet refueller trucks with single-point refueling capabilities are equipped with nozzle pressure gauges. These gauges monitor fuel pressure during single-point fueling operations, where restricting excessive fuel pressure from entering the aircraft is a crucial concern. Additional gauges may be present on your refueler truck. Some trucks possess a pump pressure gauge that allows you to monitor the pressure from the product pump. Always repair or replace defective gauges immediately – neglecting to do so could damage aircraft and compromise safety mechanisms.

The pressure gauge with spring is dampened by a liquid-filled (glycerine), so that the display is protected from vibration. All pressures are displayed in “bar” and “psi”. Additional test connections are used to check the gauges. The following pressures are read on the dashboard:

• Venturi pressure deck and reel hose
• Air pressure
• Pump pressure
• Hydraulic pressure

The ball valves for the pressure gauges should be constantly open. They should be closed only during pressure tests or when defective components are replaced.

Before installation, commissioning, and operation, ensure that the appropriate pressure gauge has been selected in terms of measuring range, design, and specific measuring conditions. Check the compatibility with the medium of the materials subjected to pressure! The corresponding load limits must be observed to guarantee the measuring accuracy and long-term stability specified. This process is essential for maintaining pressure gauge accuracy and ensuring compliance with international fueling standards.

Aviation fueling equipment shall be equipped with a pressure connection that can be used to check accuracy against a master pressure gauge without the need for removal. This design facilitates easy pressure testing and leak detection.

Types of Pressure Gauges

There are several types of pressure gauges used in aviation fueling systems, each serving a specific purpose:

• Bourdon Tube Gauges: These are the most common type of mechanical pressure gauge. They consist of a coiled tube that straightens as pressure increases, moving a needle on a dial to indicate pressure levels.
• Digital Pressure Gauges: These provide a digital readout of pressure levels, often with enhanced accuracy and additional features such as data logging and alarms. Some modern systems also incorporate digital temperature indicators for comprehensive monitoring.
• Differential Pressure Gauges: These gauges measure the difference in pressure between two points in a system, which is crucial for monitoring filter conditions and ensuring optimal performance.

Many of these gauges are now made with corrosion-resistant materials to withstand the harsh environments often encountered in aviation fueling operations.

• Understanding Corrected Differential Pressure in the Aviation Fueling Systems

The Critical Role of Pressure Gauges During Fueling Operations

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The operator monitors pressure control equipment by observing vehicle pressure gauges. If pressures exceed acceptable limits, the fueling shall be stopped. This process is crucial for fuel flow control and preventing overpressurization. Aviation fueling pressure gauges should have a range of 0 – 10.5 bar (0 – 150 psi) and be clearly visible; all gauges and valves should be readily visible from the operating position. This setup facilitates effective leak detection and ensures proper fuel flow control.

For ease of reading, faces with a diameter of 4 – 5 inches are recommended. Gauges should be checked for accuracy (+/- 2 psi) every six months using a suitable master gauge accurate to at least +/-0.5 % full scale when checked against a deadweight tester.

1. Pressure gauges should have an accuracy of ±2% of full-scale deflection.
2. Master gauges should have an accuracy of ±0.5% of full-scale deflection.

Digital pressure gauges or Bourdon gauges filled with glycerin/silicone fluid shall be used. These gauges are essential for monitoring the aviation fuel circuit and ensuring proper fuel flow control.

Measurement Gauges in Aviation Fuelling Vehicles

PCV Air Reference Gauge

• This gauge indicates the air pressure that is applied to the pressure control valve (PCV)/deadman valve.
• Gauge scale 0 – 150 PSI
• More commonly referred to as the in-line pressure control valve (ILPCV) or secondary pressure control system
• The PCV Air Regulator is set and locked wired at the controlling pressure – usually between 50-55 PSI plus spring bias of the valve
• With the deadman handle not activated, the gauge will read zero
• Activation of the deadman handle energises the deadman solenoid, which allows air to be applied to the ILPCV – needle will slowly rise (over about 5-10 seconds and should stop at the set pressure
• Considered a critical gauge

PCV Monitor Gauge

The PCV monitor gauge, sometimes referred to as the venturi gauge, indicates “simulated nozzle pressure” and is sensed from a device called a venturi.

• Gauge scale 0 – 150 PSI
• Refuelling with a nozzle pressure that is too high can damage an aircraft’s fuel system. Too little pressure means the refuelling takes too long.
• You may also notice that in its resting state, when all nozzles are stowed, the gauge reads around 10 PSI.
• This is because the thermal relief system is set to relieve down to this pressure.
• A pressure higher than 10 PSI may indicate a faulty/sticky non-return valve.
• Considered a critical gauge

Pump Discharge Pressure Gauge

• It is sensed from the pump outlet and indicates the pump discharge pressure.
• Gauge scale 0 – 230 PSI
• This pressure will vary with flow rate.
• On a typical 1000 lpm maximum flow rate fueller, it is:
  • Approximately 36 PSI at idle and:
  • At maximum flow rate can be upwards of 98 PSI
• Not considered a critical gauge – Indicator only and can assist with troubleshooting.

Hydraulic Pressure Gauge

• Indicates hydraulic system pressure.
• Like pump discharge pressure, this will also vary with flow rate.
• On a typical 1000 lpm maximum flow rate, fueller, depending on the set-up, it is:
  • Approximately 750 PSI at idle and:
  • At maximum flow rate is around 2,500 PSI
• It is not considered a critical gauge – It is an indicator only and can assist with troubleshooting.

Importance of Accurate Measurements of Pressure Gauges in Aviation Fuelling

Accurate pressure readings are vital for several reasons:

1. Safety: Over-pressurization can lead to fuel leaks, spills, or even explosions. Accurate gauges help maintain pressure within safe limits and are crucial for leak detection.
2. Efficiency: Monitoring pressure ensures that fueling operations are conducted smoothly, reducing the risk of delays and operational inefficiencies.
3. Equipment Protection: Proper pressure levels protect fueling equipment from damage, extending its lifespan and reducing maintenance costs.

Calibration Requirements

Regular calibration of pressure gauges is essential to maintain accuracy. Most regulations stipulate that:

• Gauges should be calibrated at least every six months.
• Calibration should be performed using a master gauge or dead-weight tester.
• Records of calibration must be maintained for compliance and safety audits.

Refuelling Equipment Recommended Scale

• Hydrant system pressure at inlet (servicers): 0/15 bar (0/225 psi)
• Pump pressure (refueller): 0/15 bar (0/225 psi)
• Pump negative pressure (refueller): -1/5 bar (-15/75 psi)
• Reference air pressure (on ILPCV): 0/10 bar (0/150 psi)
• Controlled pressure (in the absence of a compensated system): 0/10 bar (0/150 psi)
• Pressure at neck of Venturi: 0/10 bar (0/150 psi)
• Utility air pressure: 0/10 bar (0/150 psi)

Conventional Bourdon-type gauges or equivalent pressure gauges are classified as critical pressure gauges, for those that indicate information essential to the monitoring of the correct operation of the equipment, and for information pressure gauges. The critical pressure gauges are:

• Pressure gauge of the test rig
• Venturi pressure gauges
• Pump pressure gauges
• Hydrant pressure or input pressure gauges
• Pressure gauges of regulated pressure

The maximum error tolerated for critical pressure gauges is:

• 2% of the full range of measurement of the pressure gauge for test rig/bench pressure gauges and venturi pressure gauges
• 5% of the operational range of use for other critical pressure gauges

Pressure gauges that do not successfully pass the test shall be repaired or replaced. It is strongly recommended that information pressure gauges be tested every 6 months without a maximum tolerance of error. A pressure gauge that no longer functions or indicates excessively erroneous data shall be repaired or replaced.

• Monthly Aviation Fueling Hose Testing Requirements

Regular Inspections of Pressure Gauges in Aviation Fuelling

Conducting routine inspections helps identify potential issues before they become serious problems. Key inspection points include:

• Checking for physical damage or corrosion.
• Ensuring that connections are secure and leak-free.
• Verifying that the gauge is functioning correctly by comparing it to a master gauge.
• Performing wear and tear inspection to prevent blockages and ensure optimal performance.

Cleaning and Care

Keeping pressure gauges in Aviation Fuelling clean is essential for accurate readings. Dust, dirt, and fuel residue can affect performance. Regular cleaning should involve:

• Using appropriate solvents to clean the gauge face and housing.
• Ensuring that any seals or gaskets are intact to prevent contamination.

Training and Competency for Operators

The effectiveness of pressure gauges in aviation fueling is heavily reliant on the competency of the operators. Proper training is essential to ensure that personnel can effectively monitor and respond to pressure readings.

Operator Training Programs

Training programs should cover:

• Understanding the function and importance of pressure gauges.
• Procedures for monitoring and interpreting gauge readings.
• Emergency protocols for responding to pressure-related incidents.
• Proper use and maintenance of aircraft fueling nozzles, including both overwing nozzles and underwing nozzles.
• Familiarization with helicopter fueling nozzles and their specific requirements.

Continuous Education

Ongoing education is vital to keep operators updated on new technologies and regulatory changes. This can include:

• Workshops on the latest advancements in pressure gauge technology.
• Refresher courses on safety protocols and best practices.
• Training on ergonomic nozzle design and its impact on fuel flow control.
• Updates on compliance requirements and industry standards.

Conclusion

Pressure gauges and transducers are indispensable tools in aviation fueling, ensuring safety, efficiency, and compliance with regulatory standards. Their role in monitoring fuel pressure cannot be overstated, as they help prevent accidents and protect both personnel and equipment. By adhering to maintenance practices, regulatory requirements, and investing in operator training, the aviation industry can continue to rely on pressure gauges as a cornerstone of safe fueling operations.

The importance of pressure gauge accuracy, leak detection, and compliance with international fueling standards cannot be overstated. Regular pressure testing, leak testing, and maintenance of fueling nozzles are crucial for preventing fuel contamination and ensuring the integrity of the aviation fuel circuit. As technology evolves, the future of pressure gauges looks promising, with innovations set to enhance their functionality and reliability even further, including advancements in smart nozzle technology, digital monitoring systems, and improved fueling port compatibility.

The use of corrosion-resistant materials in gauge construction, along with the implementation of automatic shut-off valves, further enhances the safety and reliability of aviation fueling systems. Regular inspections of the hydraulic oil circuit and gearbox oil circuit, coupled with stringent blockage prevention measures, contribute to the overall efficiency and longevity of fueling equipment. The aviation fuelling test rig plays a crucial role in maintaining the accuracy and reliability of pressure gauges, ensuring that all components meet the strict compliance requirements of the industry.

• Compliance Services

As the aviation industry continues to evolve, the role of pressure gauges in ensuring safe and efficient fueling operations remains paramount. Their integration with advanced technologies and adherence to rigorous testing and maintenance protocols will continue to support the industry’s commitment to safety and operational excellence.