Building a Foam Core Powerboat

This site will report on the building of the 'Hawk41', a 41ft sea-going launch. It's specifications are: - Length: 12.50 m - Length waterline: 12.07 m - Beam: 3.27 m - Draft: 0.75 m - Displacement: 4.3 t - Engine Power: 184 kW.
The vessel will be constructed from a foam core sandwich using the 'controlled vacuum infusion' technique.

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Location: Utrecht, Netherlands

Monday, July 23, 2007

A DIY pressureswitch

Ever heard of a "vacuum advance unit"? It's a small device used in car engines.
Has something to do with the ignition moment. It is a small "can", equipped with a membrane attached to a lever. It has a tubeconnector at the side opposed to the lever. See also the picture. It can be used to make a pressureswitch yourself. Here is what I did:
I connected the vacadvance to some copper piping built in a wooden box. The vacuum pulled by my pump is applied on the unit and therefore it retracts the lever. The lever in its turn operates a switch. (See the second picture) The whole contraption can be tuned by tightening a spring.
To get some feedback I mounted the pressuregauge on top of the box.


See the third picture for the end result. It works like a charm!.....


However.... The switch has a wide range of "hysteresis". In this case it means that the points at which the switch kicks in and out are a bit too far apart. On operation the pressureswitch switches the pump off at let us say -0.9bar. It switches on again at -0.7bar. Rather wide apart.


It will do for the time being, but when another solution comes by I will give it a serious consideration.

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