Difference between revisions of "Processor pressure switch"
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<metadesc>Biodiesel processor safety, Biodiesel float switch, Biodiesel processor level switch, Washing machine pressure switch, Washing machine level switch, Using a pressure switch as a level switch, Biodiesel processor heater safety interlock, Inhibiting a Biodiesel heater, Interlocking a Biodiesel processor, Biodiesel processor controls, Processor electrics</metadesc> | <metadesc>Biodiesel processor safety, Biodiesel float switch, Biodiesel processor level switch, Washing machine pressure switch, Washing machine level switch, Using a pressure switch as a level switch, Biodiesel processor heater safety interlock, Inhibiting a Biodiesel heater, Interlocking a Biodiesel processor, Biodiesel processor controls, Processor electrics</metadesc> | ||
| − | With processors that contain a heating element in the liquid, there is the risk of | + | With processors that contain a heating element in the liquid, there is the risk of methanol vapour explosion in the following circumstances: |
* liquid level drops because of a leak while the processor is unattended | * liquid level drops because of a leak while the processor is unattended | ||
* leaving the element on when the processor is being drained | * leaving the element on when the processor is being drained | ||
| Line 31: | Line 31: | ||
[[File:Level_switch_3.png]] | [[File:Level_switch_3.png]] | ||
| − | To control the immersion a relay is required, preferably a | + | To control the immersion a relay is required, preferably a solid state selay. The switch side should be low voltage DC, say 9-12V as provided by many wall plug-in transformers. |
Suggested circuit: | Suggested circuit: | ||
| Line 37: | Line 37: | ||
[[File:Level_switch_circuit.png]] | [[File:Level_switch_circuit.png]] | ||
[[Category:Biodiesel]] | [[Category:Biodiesel]] | ||
| − | [[Category: | + | [[Category:Processor controls and instrumentation]] |
Latest revision as of 22:46, 3 March 2013
With processors that contain a heating element in the liquid, there is the risk of methanol vapour explosion in the following circumstances:
- liquid level drops because of a leak while the processor is unattended
- leaving the element on when the processor is being drained
- turning on the element when the processor is empty
To reduce the risk it is sensible to fit a deadlock on the heater element to ensure that it cannot be switched on unless the element is completely submerged.
One way to do this is using a washing machine pressure switch. These can be picked up from most white goods repair shops or online.
The pressure switch requires a tube down into the liquid inside the processor - this can either be through a port in the top of the processor or through a side port, as in this example:
The 15mm pipe by the tape measure pokes through a port in the side of the tank. The 22mm pipe is on the outside, and is long enough to prevent liquid escaping should there ever be an air leak from the flexible tubing or switch.
Here's the top, where the flexible tubing connects:
This is made from a 22mm end stop, with a hole drilled to fit a little copper insert as used to reinforce plastic piping (the 10mm kind). It's soldered in place to make it air tight.
The green elbow is just an aquarium pipe connector - it squashes the very short length of aquarium tubing that goes inside the copper insert tightly against it's inner surface. The other side goes off to the pressure switch.
The end of the 15mm pipe should be dunked into water inside a squash bottle to test it for leaks and the trip points.
This pressure level switch has two trip points with hysteresis on both, measured from the end of the pipe underwater to the liquid surface. One was at 60mm (filling) 30mm (emptying), and one at 120mm (filling) and 90mm (emptying).
Here it is fitted to the processor (next to the condenser):
To control the immersion a relay is required, preferably a solid state selay. The switch side should be low voltage DC, say 9-12V as provided by many wall plug-in transformers.
Suggested circuit:
