Situation
Tyne Pressure Testing partnered with a defence manufacturer to carry out low pressure testing, also known as altitude testing, on four units in accordance with standard MIL STD-810G.
The units, which are part of a military application, included a winch assembly, maintenance panel, variable frequency drive and a control panel. The components ranged in sizes from 500mm and 1,100mm in length, 670mm and 2,150mm in height, weighing between 70kg and 751kg.
MIL STD-810G is used in low pressure (altitude) tests to determine if a material can withstand and/or operate in a low pressure environment and/or withstand rapid pressure changes. As part of MIL STD-810G, the component is specified to fly at altitudes of below 21,300 metres and must be able to; operate at a high ground elevation site, be operated and pressurised/unpressurised in areas of an aircraft, be exposed to explosive decompression and be carried externally on an aircraft.
Approach
Due to its size, hyperbaric chamber TPT 2 was used to perform the low pressure test. Chamber TPT 2 has an internal length of 3 metres and can pressurised up to 1,450psi/100 Bar.
To mimic the low pressures of an altitude environment, a vacuum was constructed inside the chamber to decrease the pressures in order to simulate the required air pressure. Testing in this way is challenging due to the natural environment’s atmospheric pressures on the test day. If the weather is warm, the atmospheric pressure is high, where as if the weather is cold, the pressure is low, and therefore a change in the weather can affect the test. Specialist transducers were used to measure the atmospheric pressure within the chamber to verify that the air pressure required had been achieved. The atmospheric pressure in the chamber was reduced down from 1,013 millibar to 870 millibar. The specialist pressure transducer used was calibrated to measure between 750 and 1,150 millibar.
The testing involved securely setting up the equipment within the open chamber, closing the chamber to create an airtight seal. A vacuum pump was used to slowly reduce the air pressure within the chamber until the required pressure was reached. The pressure was held at the desired measure for 60 minutes and was monitored and recorded for proof of compliance.
This was a challenging and interesting project for the team to work on. Using a vacuum to mimic the working conditions was something we had not done before and I am really pleased with how well it went and the markets it has opened up for the facility.
Result
All four of the units successfully passed the test in accordance with MIL STD-810G and have been specified to be used within an altitude setting.