756 
Soi 
out-of-roundness sufficient to cause leaks. Before any cellophane disk is 
used on a gauge all ravelings and any grit on the surface should be removed. 
If any creases or pin holes are present the cellophane should be discarded. 
Line up the seven pistons in numerical order and cement on the appro— 
priate pellets, each. of which must be inscribed with the number of the pis- 
ton to which it is to be cemented, This step is done first in order to give 
the cement time to harden before using the gauge. 
NOTE: EXTREME CARE MUST BE TAKEN TO INSURE THAT THE PELLETS ARE CENTERED ON 
THE PISTONS, iF THEY ARE EVEN SLIGHTLY OFF CENTER, THE RESULTS OF 
THE TEST ARE RENDERED DOUBTFUL, SINCE THE PELLETS ARE THEN SQUEEZED 
BY THE SPRINGS. 
Place the corresponding anvils and springs beside the pistons. 
The next step consists of waterproofing the face, or exposed end, of 
the gauge. This is accomplished in the following manner. 
Place one circle of cellophane over the face of the gauge, centering 
it properly. Lay the rubbor gasket and the stecl ridge ring around the 
edges, screw on the clamp ring hand tight, and then tighten it slightly 
(1/8 of a turn) with a wrench. ‘The cellophane snould be unwrinkled. Make 
3 holes in the cellophane over the screw holes for the central plate, and 
place one drop of waterproofing on cach. Put the retaining plate on, place 
another drop on each small hole in the plate and secure the plate with the 
screws provided. The face of the gauge should now be watertight. 
The subsequent stage consists of the insertion of the pistons. Slip 
the small spring over the zero piston and insert it the entire distancc, 
using a small wooden dowel, 1/), in. in diameter and about 10 in. long. lay 
the gauge on its side and slide the remaining six pistons into their proper 
holes. Use the wooden dowel, not a sharp metal instrument which may mar the 
pellets. 
When all the pistons are installed, insert the springs. Make sure that 
no spring touches a pellet. Also insert one copper ball and its centering 
washer in the zero channel, Slide —— do not drop — it in. 
Now place the six anvils in their corresponding holes, and screw on 
the cap, It will be necessary to hold dowm anvils h, 5 and 6 with a plate, 
such as the blade of a putty Imife. 
The final stage consists of waterproofing the top, following the same 
procedure as that outlined for the momentum gauge. 
When the retainer plate, the pistons, and sometimes the gauge body 
develop sharp edges which bear against the cellonhane disk, puncture of the 
cellophane is likely to occur, On new gauge parts sharp cdges are prevalent. 
To prevent leaks from any such punctures these parts should be polished 
smooth with crocus cloth. The same precautions for maintaining watertight— 
ness which apply to the momentum gauge also apply to the Hilliar gauge. 
