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MMD > Archives > July 1997 > 1997.07.23 > 13Prev  Next

Vacuum Gauge Construction
By Darrell Clarke

G'day Richard,  Replying to your request:

> Could you post the instructions for building a water gauge for
> measuring player piano vacuum levels?  Thanks much.

A water gauge is very easy to construct, the only problem is the height
of the thing if you want to read up to 60" full vacuum -- it must be
higher than the full vacuum to be measured!

Mine reads up to 48" so I have to be careful not to apply higher vacuum,
so beyond this is where a mercury or dial gauge is handy.

Basically, it is "U" tube of clear vinyl tubing of about 6 mm (1/4")
diameter loosely attached with staples to a lightweight wooden board
about 100 mm X 1.4m (4" X 4' 6") so that some vertical adjustment is
possible.  Use at least 2.5 times the full reading height for the tubing
length.  An inch scale is marked or attached to the board to measure the
height differential of coloured water half filling the tube.

A fixed scale would be calibrated 1/2" to the inch (2:1) to measure the
rising height of one leg but a more accurate measurement can be made with
a moveable inch scale to measure the full height differential between
both legs.  The disadvantage of the latter method is the need to set the
scale for each measurement and I find the fixed scale more useful.

Fill the tubing to the halfway point with water and food colouring by
sucking from one end with the "instrument" at an angle and adjust the
loop at the bottom and/or scale until the level matches the zero point of
the fixed scale.  Either end can be used for both suction and pressure
measurement.  Attach a suitable length of tubing to one side, with size
adaptors if needed, to connect to measuring points on the player.

Things to watch out for:

The scale must be as near to vertical as practical.  A base will help
here.  A trap using a glass jar might be necessary if there is a risk of
exceeding the full height vacuum.

The water might tend to cling to the inside of the tubing and break up
into drops.  Oscillating the column by sucking can pick up the drops, but
using less "clingy" tubing will help.  Too small bore will make it worse.

There will be some inertia in the water columns so that accurate
measurements can only be made on static levels, although it is useful to
monitor relative dynamic changes for continuity and smoothness.

Close off the ends when not in use to reduce evaporation.

I hope this is of use to you.


Darrell Clarke

(Message sent Wed 23 Jul 1997, 02:15:00 GMT, from time zone GMT+0930.)

Key Words in Subject:  Construction, Gauge, Vacuum

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