D2 gas leak valve with remote control.

[Rich Gorski]

One of the problems running a fusor is balancing the chamber D2 pressure with the voltage applied to the grid. The idea being to have a stable condition where the current level remains steady. This often requires frequent adjustment of the D2 leak rate into the chamber. In my system as in most the leak valve is positioned very close to fusor so the length of gas tubing from the valve to fusor is minimum. This however require the operator to shut down the high voltage every time the gas valve needs to be adjusted so exposure to X-rays (and neutron flux) is minimized. It would also be great to be able to adjust the gas flow while the unit is operating so I can watch the result of change in pressure in real time on the monitor. This situation prompted me to install a remotely operated motor on the gas leak valve.

The valve is driven by a 6 RPM, 12VDC, reversible, high torque motor from Amazon with a torque rating of 25KG/cm. This high torque can easily turn the shaft on the valve from fully closed to fully open. The valve is a Dakota Instruments Barstock metering valve with a 16 turn- non rising stem and a 0-1000 ml/min (air) flow rate range. One of the issues with remote control of the valve using a motor is that the force on the valve stem and motor can become excessive if driven past the full open or full closed points. To handle this I added a current meter to monitor motor current. During steady rotation, the motor current reads a steady 0.050A but when it nears the end of the travel the motor starts to feel more resistance and the current rises. That current rise is the signal to stop the rotation as it is near the end of the travel.

The motor and valve both have ¼” shafts and are connected by an aluminum coupling fixed with set strews. The entire gas system including PEM cell, thermoelectric chiller to remove moisture and motor/valve are shown in the photo below. The PEM cell from H-TEC Education has a peristaltic pump to circulate heavy water through the cell. 2 ml of D2O will keep the cell running for 2 or 3 hours producing D2. In the upper portion of the photo the control box with 12 volt battery for power supply is visible. The blue readout is the motor current monitor. Ten feet of cable attach the control box to the gas system which brings the control box to the operator station.

Parts:
Leak valve: Dakota Instruments Barstock metering valve model 6AMV2103: 0-1000ml/min flow range (air). $167
Motor: Amazon, Bringsmart, 12V, 6 RPM worm gear motor, Torque 25kg/cm. $14.44

[Dennis P Brown]

Nice design.

I have found that the leak valve control is both critical and very sensitive to achieving a stable plasma in a fusor. Being able to quickly adjust the plasma via the valve (current is exactly coupled to this valve) makes fusor operation far easier. I have shielding so the issue of operating near the fusor isn't a problem. Through I run at a lower voltage range then many here so x-rays don't pass my steel walls; through I have further slate shielding (and neutron shielding as well.)

[Jerry Biehler]

You can use a piezoelectric leak valve. They use a variable voltage around 0-100vdc to control the leak rate.

[Rich Gorski]

Yeah, when the time comes to replace my current valve I would try to find a used piezo type like the Key High vacuum PEV-1. They are expensive new like $1000 but there was one on ebay going for $297. For now this motor driven setup work fine for my use.

Rich G.

[Alexey Khrushchev]

Rich, I use the exact same motor to control the rate of deuterium flow into the chamber. I also use a driver with a PWM modulator for finer tuning. This reduces the motor shaft speed by another factor of 10. In addition, the driver has a reverse button to quickly change the direction of rotation. I also printed on a 3D printer a device for quick removal of the motor, this allows me to use the motor only for fine tuning the deuterium flow, and I close the valve by hand after the motor is removed.

However, you should be aware that there is a risk of electric shock when using such a remote. The point is that the motor is under the potential of the chamber (ground) and the wire from it goes to the remote control. In case of several unlikely events (ground breakage, plasma breakdown on the chamber body) the operator can be electrocuted when touching the buttons of the remote control. That is why I always use protective gloves when adjusting the pressure in the chamber.

[Rich Gorski]

Great cheap little motor isn't it? I've got mine running on pure DC and I can control the motor speed by adjusting the voltage from about 6V up to maybe 18 volts and a simple switch to change direction. At 6 volts it barely turns at all but still has enough force to turn the valve. That along with the leak valve I chose seems to offer me good control over the chamber pressure and from behind the control console. I have enough control to easily change the pressure from 5x10-5 Torr to 6x10.5 Torr and that is way lower than what is needed to create a plasma. And in the 10-3 pressure it takes several turns to go from 10-3 to 10-2.

As for the possibility of high voltage getting back to the control console, I'm have no concerns because my stainless steel chamber is connected directly to earth ground (water pipe) through a 4 AWG copper cable. So its well grounded. I suppose one could worry about an arc between the air side of the HV feedthrough going to the motor but with the way things are positioned in my system (several feet) I doubt that would ever happen.

Rich G.