753 
APPENDIX IIT 
Use of the Hartmann Momentum Gauge 
[Adapted from Navy Department, 
Burd (RE2c) Technical Note No. 15.] 
Arrangement of the gauge: The gauge, when ready for operation, consists of 
the following picces: 
1. The body of the gauge, into which all the other pieces fit. 
2e The cap of the gauge, which screws into the body of the gauge, and 
also into the mounting cape 
3. The piston, into which all the remaining pieces are placed. 
he The copper pellet, which should be 0,500 in. long. 
5 The rubber washer, which centers the pellet in the cavity provided 
for it on the piston, 
6. Two small cylindrical stop pins, and a spring, which fit into a 
cylindrical hole extending horizontally through the piston, 
In additon to the item present in the gauge, certain additional devices 
are required to assist in the assembly of the gauge. These are mentioned 
belove : 
Preparing the gauge for usc: 
1. Copper pellets should be selected from lots of uniform hardness and 
diameter, and the length of cach individual pellet should be recorded to 
0.0001 in, 
2e Determine the number of gauges to be used in the test. Procure that 
number of each of the six pieces or sets of picces described above, Be sure 
all parts of the same gauge bear the same serial: number. 
Check to be sure the piston travels freely in the gauge. 
Be sure spring catches do not stick in the body of the gauge. 
3. Arrange the items in rows as follows: 
In the row farthest from the operator place the bodies of the gauges 
with the small opening upward. The purpose of arranging the bodies upside 
down is to provide a stand for the pistons, Place the appropriate piston 
in the corresponding hole, so that the large part of the piston rests on 
tne bottom of the gauge body,» 
Sree 
