I have two out-of-print books written as instructional guides for apprenctices in the steam fitter/pipe fitter trades which provide illustrations and give descriptions for installing DP orifice meters (among others).
1) "Instrumentation & Process Control" for Steamfitter Pipefitter Journeymen and Apprentices, a softcover published by the NJS-PAC National Joint Steamfitter-Piprfitter Apprenticesip Committee in a later editions around 1980. No ISBN number
2) The other is "Industrial Instruments and Control Piping" for Steamfitter - Pipefitter Journeyman and Apprentices, printed the Merkle Press (Washington DC), publishd by National Joint Steamfitter-Piprfitter Apprenticesip Committee, a hardcover, no ISBN number, from 1961 or 1967.
They are merely different editions using the mostly the same diagrams and data.
Copies appear on occasion on eBay or on ABEbooks.com for about $25.
Regarding seal pots, the books divide installation into 3 categories, gas, liquid and steam.
The instruments illustrated are pneumatics.
Text from 1) above:
Steam Flow Measurement. Direct. The measurement of steam or other condensable vapors requires the use of condensing chambers to condense the vapor and provide equal liquid heads on both sides of the meter. It is important that these chambers be mounted at equal levels (elevation), and that the lines between them and the meter be solidly filled with liquid. Steam meters should, if at all possible, be mounted below the line. Figure 11-63 shows a recommended piping system. Recommended piping size is as follows:
0-15 ft - 3/8 in copper tubing or
1/4 in brass pipe
15 to 50 ft - 1/2 in brass pipe
above 50 ft - 3/4 in brass pipe
(for pressure up to 250 psi)
Figure 11-64 shows the method of mounting seal chambers in a vertical line. When radius or pipe taps are used, the low pressure connection to the condensing chamber should be one inch pipe, as shown in figure 11-65. The larger pipe is to permit free counterflow of steam from the line, and condensate to overflow from the chamber.
Figure 11-66 shows piping for pressures above 250 psi. When pressure exceeds 600 psi, steel tubing size should be increased to one-half inch or five-eights inch. Where meter lines must "duck" existing piping, vapor traps and sediment traps should be used as shown in 11-67.