DIAPHRAGM GAS METERS
1. INTRODUCTION. Diaphragm meters are used only for gas metering. The
principle elements of a diaphragm meter are flexible partitions or diaphragms
of the measuring compartments, valves for controlling and directing the gas
flow in filling and emptying the measuring compartments, appropriate linkage
to keep the diaphragms and valves synchronized, register for counting the
number of cycles, and maincase to house the components. To obtain continuous
flow and power to operate the register, it is necessary to have three or more
measuring compartments or chambers, with two or more movable walls. These
walls are sealed with a flexible material that is impervious to gas. Movement
of the walls or diaphragms are so regulated that the total displacement on
successive cycles is the same. The amount of travel or stroke of the
diaphragms is regulated in most meters by the radial position of the crankpin
that the diaphragm linkage arms are attached to. Figure 4-7 shows the
sequence for filling and emptying a meter that has two diaphragms and four
measuring chambers. The most common unit of measurement for these meters is
cubic feet. Diaphragm meters are available to fit pipe sizes up to 4 inches,
with a maximum capacity of 12,000 cubic feet per hour.
Any shock, excess jarring, tipping, or turning upside down of the
meter or regulator may cause internal damage, resulting in
equipment failure or inaccurate measurement.
Diaphragm meters must be installed in the flow line, upstream of any activity
or outlet they are monitoring. Always check manufacturer's instructions prior
to installation for the proper methods of handling, storage, transit, and
installation. When installing a meter, be sure the following checks have been
made and the indicated items are available.
(a) Securely restrain and properly cushion meters during transit to
prevent tipping and excess jarring.
(b) Keep meter hubs covered and protected until ready for installation.
(c) When a separate pressure regulator is required, keep inlet and outlet
plugged and protected until ready for installation.
(d) Ensure that the inlet piping is clean and does not contain any pipe
scale, chips, rust flakes, or other foreign materials.
Installing meters in a tilted position may cause inaccurate
meter operation and registration.