ElectraTherm Safety Valve

Project Overview

ElectraTherm’s Green Machine product currently utilizes a pneumatically actuated valve system to assist in process control.  A detailed description of ElectraTherm’s Green Machine is given in the video below.

Given that the system is pneumatically actuated, every Green Machine must be outfitted with a compressor to operate the valve system.  Operation of the compressor increases the number of rebuilds a machine will experience over the life of the machine, requiring additional time and money  ElectraTherm spends through continued maintenance.  Additionally, due to the nature of pneumatically actuated valves, the compressor is required to remain in an operational condition, providing pressure to the valves when the Green Machine is turned off thus, consuming power.

ElectraTherm’s ultimate goal is to simplify the system by eliminating the compressor by converting the valve actuators to electronic actuators.  As a result of eliminating the compressor, ElectraTherm plans to reduce cost and required maintenance by increasing the reliability of the Green Machine.

Concept Overview

The design concept that the team came up with is driven by an electric motor that turns a pinion gear  to displace the rack gear, the rack gear then opens the valve.  To keep the motor from constantly being powered on an electromagnet will be attached to the rack, this will hold the valve open as long as the system is on without the motor running.  The return system uses  springs to return the rack to its original position.  When the system is shut down the electromagnet will lose power and stop holding the valve open and the force stored in the spring from the rack’s displacement will take over and return the rack to its original position and in doing so the valve will close.  A computer model of the system is shown below.  The larger gray cylinder represents the electric motor, the smaller gray cylinder is the pinion gear, the red L shape is the rack, the blue spring represents both the spring and the electromagnet, and the yellow pipe with the ball is the valve.

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Proof of Concept

Team ETSV’s proof concept is the electromagnetic catch system. The team tested this concept because it is not a common method used in the industry and is unfamiliar to the team. A test structure was built out of wood, allowing the team to apply the maximum rated weight safely.

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The weight simulated an applied spring force, and the test simulated the valve closing so that the team could measure system lag and any residual magnetic forces after power is cut off. This helped the team determine if the electromagnetic catch system was plausible and helped choose type of spring that should be used.

As a result of testing, we found that response times of the electromagnets we are interested in could range from 0.50 – 2.0 seconds for weights below 10 lbs, while response times of less than 0.10 seconds were achieved for weights greater than 20 lbs.

Armed with this information, we felt confident that applying an electromagnet allows us to safely maintain valve position throughout the operation of the Green Machine.

Design Overview

ElectraTherm’s GreenMachine uses a hot working fluid to turn an expander, which in turn runs a generator to create electricity.  For safety concerns when the machine is off the fluid must bypass the expander to avoid serious injury when working on the machine.  To accomplish this ElectraTherm designed a bypass route for the fluid when the machine shuts down.  Bypass is accomplished by two valves and actuators, one actuator closes one of the valves and blocks fluid flow to the expander and the second actuator opens the second valve to allow the fluid to flow through the bypass system.

The design team was tasked with improving the current actuators in use by ElectraTherm.  The team’s design uses the current actuator as the basis for its improved actuator.  The current design is driven by an electric motor, held in operating position by electromagnets, and returned to normal by a spring return system.  The improved actuator meets all of the design specifications given to the team by our sponsor.  The computer model of the prototype is shown below.

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Using the current actuator as the base for our design we have ensured the desired 1 second close time for safety in an emergency situation.  By using a 120 volt 6 revolution per minute electric motor the new design meets the requirement of updating the actuator from pneumatically powered to electrically powered with a controllable actuation speed.  Using the electromagnets to hold the valve in operating position provides a fail-safe catch design,  if power is lost to the machine the valves will automatically return to their normal bypass position.  The design uses a modified Geneva Mechanism attached to the drive shaft of the motor and the driven shaft of the rack and pinion to turn the actuator exactly 90 degrees.  This pushes the pistons and compresses the springs to put the actuator in operating position.  Once operating position is achieved the striker plates that the team designed and attached to the pistons make contact and are held to the electromagnets.  There are two electromagnets, one on each side of the housing to provide more than enough force to hold the compressed springs.  The electromagnets are held in aluminum housings designed by the team that bolt directly to the current actuator by using the team’s redesigned spring cap.  By using the current actuator as a base for the design the team has created an improved actuator that can be a full retrofit to all of the machines that are already in operation in the field and can be newly manufactured to be implemented on any new machine built in the future.

Fabrication

The housing:  For the electromagnet housing and the spring retaining caps we chose to use aluminum for strength and lack of magnetic interference.  The parts were designed in SolidWorks and then the drawings were sent to our fabricator.  These parts are shown in the picture below.

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The catch system:  The catch system utilizes striker plates and striker plate rods attached to the pistons on the rack and pinion system being held in place by electromagnets.  These catch system parts were made out of stainless steel to be as strong as possible and to be easily attracted by the electromagnets.  Below shows the striker plate catch assembly.

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This is Patrick machining the Striker Plate Rods

The drive system:  Our drive system consists of an electric motor and a pinion gear attached to a modified Geneva mechanism to power the actuator.  The electric motor was sourced from Grainger Industrial Supply.  The Geneva mechanism parts were made out of aluminum for strength, cost, and quickness of machining purposes.  To allow the team to use aluminum in the driving mechanism a stainless steel fitting was pressed inside of the Geneva mechanism to take the majority of the load.  The pin on the driving part of the Geneva mechanism is also stainless steel to account for the large force held by that small part.  After a testing mishap we also had to fabricate the driven portion of the Geneva mechanism with a star interface to distribute the load more evenly and to prevent further damage to the prototype.  Below are the parts of the actuator’s drive system.

15_21_GenevaThis is the Geneva Mechanism used to drive the actuator with the motor

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These are the team’s redesigned Star Interface

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This shows the full drive system, from top to bottom: electric motor, motor mount/Geneva housing, and the geneva mechanism.

Miscellaneous parts:  To complete the prototype and put all of the above parts of fabrication together the team had to do a little bit of fabrication of miscellaneous parts.  First the team used a rod of nylon and a lathe to create a bushing for the Geneva mechanism to ride on to reduce play in the system and reduce resistance.

15_21_bushinglatheThis is the machining of the nylon bushings

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This is the finished product of the nylon bushings

The second part that had to be fabricated to complete the prototype was the Geneva mechanism housing/motor mount.  The team designed a simple rectangular housing with the tolerances necessary for our Geneva mechanism to function properly and with bolt holes for mounting to the actuator and motor.  The rectangle was left open on the sides purposefully and then covered with Plexiglas so that the team could safely demonstrate and present our driving mechanism to people.  The motor mount can be seen above in the picture of the drive system.

Prototype

Through the course of the academic year the team designed, fabricated, tested, and presented a prototype of an electric valve actuator made to the specifications of our sponsor, ElectraTherm.  When the project was completed all of the specifications were met and the testing indicated that the prototype could safely be used in its intended application.  The prototype is capable of being in continuous use, can handle temperature extremes, and will return the valve to normal in under one second.  The project was well received by students and professors at the University of Nevada, Reno, the team’s sponsors, and the engineering professionals that attended the University’s annual Innovation Day.  Below you can see a picture of the completed prototype as well as a video of it in operation.

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Meet the Team

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Patrick Stampfli

Patrick is a senior in mechanical engineering. His background in the welding industry will bring organization skills to the group and assist in meeting deadlines. Also, his technical background will be helpful when in the design and prototype phase of the project. Patrick works well with teams and will play an essential role throughout the project.

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Justin Brown

Justin is a senior mechanical engineering student at the University of Nevada.  He has a background in automotive diagnostics, repairs, and modifications.  His hands on experience will help in aspects of the design phase and in the building phase of the project. Justin’s interpersonal skills will help to maintain healthy team communication and a focus on project completion.

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Cesar Ruiz

Cesar is a senior currently majoring in mechanical engineering. He would like to pursue a career with many different projects and that focuses on mechanical aspects of its system. Enjoys creating autonomous systems such as things found in the robotic area of study. He is productive in taking time to help on a required project.

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Ian Chase

Ian is a senior studying mechanical engineering at the University of Nevada, Reno, in addition to seeking a minor in Unmanned Autonomous Systems. He has experience in product development and cost estimating in the investment casting industry. Ian’s understanding of customer interactions and team dynamics will support a productive atmosphere throughout this project.