Making and removing a bubble


If you were to open your Mk IX you would see in the left half of the instrument the bubble chamber assembly. The left hand drawing above shows a view from directly above the chamber when it is in a normal (vertical) operating position. The right hand sketch shows the view as seen through the eyepiece, I have exagerated the size of the drilling just to give you some idea of it's position.

To check the bubble:- Position yourself under a source of light so that light comes through the frosted window with an open shutter on top of the instrument. Set in maximum sun shades so a minimum of light comes in through the front. Look through the eye piece. You should see a circle. There may or may not be a visible bubble in this circle. The bubble chamber forms a "Bulls Eye" type of level, not a standard tubular "Builders" level. The bubble will centralise when the instrument is vertical. You will notice at about the 10 O'clock position a small notch. If you have a large bubble in view, lean forward and to the right so this notch is at the 12 O'clock position. Now wind in and out the diaphragm knob gently, the bubble of air should leave by the notch, which is actually a tube into the reservoir and should be replaced by liquid. To generate a bubble stand the instrument vertical and turn the diaphragm knob clockwise, This will increase the volume under the diaphragm dragging fluid from the reservoir till it is exhausted and air above it is drawn in forming a bubble. Take care not to force anything.







Checking a Mk IX

Common problems