Nitrogen Service Carts are a type of self-contained aircraft ground support equipment (GSE) used to supply nitrogen for various aircraft maintenance procedures. Nitrogen is often used to fill aircraft tires and service aircraft jacks, accumulators and struts as it is an inert gas and will not react with other chemicals or metals.
Nitrogen Service Carts are used to easily transport the nitrogen bottles to and from the aircraft. They can be hand-pulled or towed behind a vehicle. They typically have a counter-balanced bottle rack that can hold between 2 and 4 compressed nitrogen bottles of various sizes and allow a single operator to easily load and unload the bottles.
Complete nitrogen carts have a control manifold that contains high and low-pressure regulators and pressure gauges used to monitor both the supply pressure in the bottles and the outputs of the regulators. A booster system is also installed on many models that can create pressures of up to 4000 psi. The carts also have hose kits to connect the regulators, boosters and bottles and provide storage to house the delivery hoses and connectors required for the specific maintenance functions.
Nitrogen Service Cart Maintenance Requirements
To ensure that the Nitrogen cart operates properly, periodic maintenance needs to be performed within the manufacturer’s designated time frames. The most common maintenance procedures are:
Before any new nitrogen bottle is installed, the O-ring seal at the bottle nipple connector should be visually inspected for cuts or deformation. After the new bottle is installed, a leak test should be performed with a soap solution to test the seal on the new bottle.
All hoses should be visually inspected for cuts or other damage every 90 days.
Every 6 months, the tires and wheel assemblies should be inspected. The tires should be visually inspected for tread wear, cuts and for damage to the valve stem or wheel rim. The tire pressure should be checked and inflated to the appropriate value. The wheel bearings should be inspected and repacked as necessary.
A leak check should also be performed on the manifold system connections between the pressure gauges, regulators and hose connections. To perform the leak test, a soap solution should be used on the connections with the system slightly pressurized with the output valves closed.
The high-pressure relief valve should also be checked every 6 months to ensure that the valve vents at the appropriate maximum pressure limit.
Nitrogen Service Cart Pressure Gauge Calibration
The pressure gauges that monitor the regulator pressures must also be calibrated regularly for the gauges to maintain their manufacturer’s accuracies.
Irregular or improper calibration of the gauges will significantly increase the out-of-tolerance conditions for the gauge which could lead to damage to the aircraft and can pose a danger to the maintenance personnel. The FAA can also levy fines or remove the equipment from service if the gauges are found to be outside of their calibration due dates.
The most common calibration interval used for the gauges is either 6 or 12 months. Those intervals conform to the manufacturer’s and industry standards and align with the maintenance intervals for the overall cart. The established calibration interval should be maintained as part of the maintenance organization’s quality management system.
Pressure gauges not calibrated after 12 months can be prone to errors due to drift and internal mechanical inaccuracies. Errors can also occur due to over-pressurization of the gauges.
The gauge accuracies are checked by applying accurately known pressures throughout the range of the pressure gauge and comparing the gauge reading to the calibration standard. The calibration standard used is typically either a more accurate gauge of a similar pressure range or a highly accurate dead-weight tester.
The damping fluid level in the gauges is also inspected during the calibration and is refilled with glycerin when needed.
can perform all maintenance, servicing and calibration of a wide variety of Nitrogen Service Carts. For more information on our GSE maintenance capabilities, contact e2b calibration.
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