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 CHAPTER 4.
POSITIVE DISPLACEMENT AND COMPOUND METERS
OSCILLATING PISTON AND NUTATING DISK METERS
Section 10
1. INTRODUCTION. Oscillating piston and nutating disk are the most common
type meters used for residential water service. They are essentially equal in
performance and have an excellent combination of accuracy, long life, simple
design, moderate cost, and ease of maintenance.
1.1 Oscillating Piston Meters.
1.1.1 Meter Design--Oscillating piston meters (Figure 4-1) are available in
nominal sizes up to 4 inches , with a maximum capacity of 500 gallons per
minute. The operating and physical characteristics of these meters are listed
in tables 4-1 and 4-2. This type of meter is commonly used for measuring cold
water, but models are available for use with fuel oils and liquified petroleum
gas (LPG).
1.1.2 Operating Principles--The main components of an oscillating piston
meter are maincase, measuring chamber, and register. As liquid flows through
the meter strainer and into the measuring chamber (Figure 4-2) it drives the
piston. The piston oscillates around a central hub, guided by the division
plate. The motion of the oscillating piston is transferred to a magnetic
assembly in the measuring chamber, which drives a follower magnet. The
follower magnet drives the register geartrain, which translates the number of
piston oscillations into units of total volume that are displayed on the
register dial. The unit of measurement must be specified as either gallons,
liters, cubic feet, or cubic meters.
1.2 Nutating Disk Meters.
1.2.1 Meter Design-Nutating disk meters (Figure 4-3) are available in
nominal sizes up to 6 inches, with a maximum capacity of 1,000 gallons per
minute. The operating and physical characteristics of these meters are listed
in tables 4-1 and 4-2. This type of meter is commonly used for q easuring cold
water, as well as chemical additives and mixture ingredients,
1.2.2 Operating Principles --The basic components of a nutating disk meter are
maincase, measuring chamber, and register (Figure 4-3). As liquid flows
through the meter strainer and into the measuring chamber it drives the disk
(Figure 4-4). Movement of the liquid around the measuring chamber, first
above and then below the disk, imparts a nutating motion to the disk (nodding
in a circular path without revolving about its own axis). A shaft that is
perpendicular to the disk extends from the top of the central ball of the
disk. As the disk nutates, the top of the shaft moves in a circular path and,
by engaging a crank, operates the meter register. The unit of measurement
must be specified as either gallons, liters, cubic feet, or cubic meters.
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