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.
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.
(e) Ensure that the meter is installed plumb and level.
(f) Check for meter shutoff valve on inlet side of meter.
(g) Check for adequate supply of meter connection gaskets.
(h) Ensure that location of meter provides proper protection from traffic or other hazards that may be present.
Operating Cycle, Four-Chamber Diaphragm Meter
FIGURE 4-7. Operating Cycle, Four-Chamber Diaphragm Meter
If remote reading or electronic transmitting devices are used, install in accordance with chapter 10 and the manufacturer’s instructions.
MAINTENANCE: The following inspection schedules are adequate for average installations.
1. Monthly Inspection: In addition to any instructions provided by the manufacturer, inspect meters monthly for the following conditions:
(a) Noisy operation of meter.
(b) Smooth movement of register.
(c) Leaks (repair if necessary).
(d) Cleanliness of glass cover on register dial (clean as needed).
2. Annual Inspection: In addition to the inspections in paragraph 3.1, inspect meters annually for the following conditions:
(a) Proper alignment and position in accordance with installation instructions.
(b) Cleanliness of meter box, housing, or pit, if one exists (clean as needed)
A schedule for cleaning and repairing meters is necessary, and should be based on the manufacturer’s recommendations.
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