Multi-tube manometer

Many pressures can be measured simultaneously with a multi-tube mano­meter (Figure 1.5), having one or more dozens of tubes connected to a common tray connected to a reservoir open to the reference pressure. For convenience, the reference pressure is also applied to one tube (or rather to the two extreme tubes of the manometer) to allow zero adjust-ment. Tubes are laid side by side on a solid table provided with a scale and covered by a sheet of protective glass or plastic that is usually also provided with a scale: the double scale serves to eliminate the error of parallax. The position of the reservoir is adjustable and sometimes the table can be rotated; the inclination of the table can be read on a circular scale.

To reduce the test time, especially in intermittent wind tunnels, a means of freezing the readings of the many tubes is needed; an example can be seen in the side view of the multi-tube manometer of Figure 1.5: it consists of an eccentric placed at the top of the pipe manifolds which, when rotated, squeezes the rubber tubes, thereby blocking the pressure in them. Alternatively, results can be frozen with a camera.