Accuracy and repeatability in valve leak test stands are key to space exploration

Exploring the final frontier

At Alicat, we work on a variety of aerospace applications, projects and experiments which help keep pilots safe, put satellites into space, and launch rockets. We work closely with our customers in these fields to understand their problems and find straightforward solutions to ensure mission-critical components and life-support systems are functioning as desired. In addition to tests stands for valve leaks and component characterization, flow and pressure instrumentation is utilized for a wide variety of tests and processes. Alicat has worked on projects that include:

  • Ensuring the oxygen masks in military and commercial airplanes flow the correct amount of gas and meet safety regulations, using bidirectional mass flow controllers to simulate human breathing while monitoring system pressure.
  • Flowing water to support and monitor cooling systems in pressure suits and propulsion systems, using liquid mass flow instruments customized to be lightweight and compatible with space suits.
  • Controlling the lift of high-altitude balloons which are used in experiments to study and understand weather patterns and various aspects of the upper atmosphere, using mass flow controllers to fill the balloons with hydrogen or helium.
  • Assisting with the pitch, roll and yaw on a rocket launch delivering an astronomical telescope satellite, using pressure controllers with high resolution control and smooth ramping to aim the scope without allowing the imaging system to blur.
  • Testing instrument performance in harsh Martian conditions, using combined mass flow and pressure control to replicate the atmosphere on Mars.

Valve leak test stands and characterization for rocket engines

Leak testing takes place in a lab environment on Earth, using test stands including mass flow and pressure controllers which can detect extremely small leak rates and volumes. These controllers, however, are generally used for pressures lower than those experienced by rockets launched into space.

Rocket components must be tested to much higher pressures – more similar to the pressures found in oil & gas process applications than in lab environments.

Dome-loaded regulators, which can handle high pressures and high flow rates, are therefore often used to control pressure in testing rocket components. But while these dome-loaded regulators can manage high pressures, they suffer from significant hysteresis due to the mechanics of the valve spring and the changing behavior of the valve depending on whether it is opening or closing. This can result in a non-repeatable process.

The Alicat solution: repeatable proportional control

3000 PSIG pressure controller that can be used in valve leak test stands

3,000 PSIG dual-valve pressure controller

To avoid hysteresis and ensure that the testing process is repeatable, Alicat provided high pressure-rated, dual-valve pressure controllers (PCDs) which can control pressures up to 3,000 PSI. To do so, the PCD uses a proportional control valve controlled by onboard PID tuning, which results in a solution much more repeatable than those offered by other pressure regulators. PCDs can also be configured with a remote pressure sense port to measure the pressure at the location of regulation, regardless of where the PCD itself is sitting. This allows for reducing the delay and speeding up the response time of the system, giving real-time data on the leak test.

To characterize and leak check the valves used for space flight, the high pressure PCDs were used to control static and flowing processes and paired with a low pressure-drop Alicat flow meter. While the PCD controlled the high pressure at the inlet port of the valve being tested, the flow meter installed downstream was capturing the leak rate through the valve.

Advantages of the Whisper-Series flow meter include that it is a non-restrictive flow device, which is necessary since the valve is exhausting to near-atmospheric pressures and the back pressure in the system must therefore be minimized. The meter was is also able to quickly easily switch between measuring nitrogen and helium gases (the most common gases used in these leak tests) and maintain its accuracy without requiring recalibration.

To meet the needs of the industry, all Alicat pressure and mass flow devices can be configured with AS5202 ports, for easy integration into a valve leak test stand or other pieces of equipment.