Commercialization of Space Provides Opportunities for Innovation:

The Use of Permanent Magnets

The commercialization of space in the United States has created a competitive market in a sector where qualified, incumbent designs were, previously, difficult to displace. The creation of new rocket systems has driven newer and more innovative designs. These designs also carry with them valuable ‘lessons learned’ from their predecessors. Valcor Engineering has recently had opportunities to create innovative and competitive solutions. One such design is a pilot-operated, pressurization valve that is utilized on first stage rockets.

The challenges of designing a component for first stage performance are manifold. Weight, vibration, temperature, leakage, response time and envelope drive the design. Often times, these requirements are in direct competition of each other.

For example, a high vibration environment requires a high holding force for dynamic components. This directly affects valve weight and envelope. Large temperature ranges can limit material selection, which can preclude certain design approaches.

The piloted valve offers fast, repeatable response time with minimal weight in a high vibration environment. There are many facets of the design that are innovative, but this paper will focus on the use of permanent magnets.

Permanent magnets offer several advantages when integrated into solenoid designs. Specifically, reduced power consumption, lower weight, and the ability to withstand high vibratory environments. For this particular design, permanent magnets were integrated into the pilot solenoid assembly as an approach to address a high vibration environment. In a typical spring-mass system, the spring and mass will have a response to any outside excitations. There are challenges to ensuring that the natural frequency is outside of the vibration spectrum. If the spring-mass system displacement becomes large or achieves resonance, then the valve may leak or fail. For this design, the mass is the pilot plunger and the spring is the holding spring.

Simply increasing the spring force to increase the required holding force will directly increase the valve solenoid weight and size, because the solenoid must overcome this larger spring force. Furthermore, the valve plunger diameter needs to increase to prevent magnetic flux “choking.” However, there is a saturation point reached for the magnetic material of the plunger and thus any additional increases in plunger diameter are not beneficial. These changes will increase the mass portion of the spring-mass system and the resulting valve design becomes untenable.

Enter the Permanent Magnet

When a permanent magnet is introduced into the magnetic circuit it will add additional plunger holding force without adding to the pull-in force requirements of the solenoid, and thereby not increase the plunger diameter. This will increase the maximum vibration envelope that a plunger-spring system can withstand. The graph shown in Figure 1 shows the increased benefit of adding the permanent magnet.

The permanent magnet moves the design into a maximum G level envelope that is double that of a spring-plunger design without a magnet. Another significant feature of the permanent magnet is that it has no natural frequency and therefore behaves optimally in a high vibration environment.