Dwyer CPF - Manual (Page 4)

Material
PVC/CPVC
pf
VARIES*
df
VARIES*
* “Average” for these floats is f = 3.50, df = 217.8.
EXAMPLE: Using a standard brass meter scaled for water (s =
1.00), what is the conversation factor for an oil with a specific
gravity of 0.85?
CORRECTING READINGS FOR NEW GAS CONDITIONS
Qg = Qs
Where:
Qg = SCFM, corrected to new conditions.
Qs = SCFM read on meter scale.
Pg = Operating pressure, psia (psig + 14.7).
Ps = Pressure stated on scale, psia (psig + 14.7).
Tg = Operating temperature, absolute (°F + 460).
Ts = Temperature stated on scale, absolute (°F + 460).
pg = Specific gravity of metered gas.
ps = Specific gravity stated on scale.
1.00 (8.30 - 0.85)
0.85 (8.30 - 1.00)
Qa = 1.00 x = 1.096
Pg x Ts x ps)
Ps x Tg x pg)
64.7 x 1.00 x 530
114.7 x 1.378 x 560
Qa = 1.00 x = 0.522
5.879
Sv
Mfh = Qm
EXAMPLE: If using a standard meter scale for SCFM Dry Air @
100 psig, 70°F on argon (SP. GR. = 1.378) at 50 psig, 100°F.,
what would the conversion factor be?
Thus, actual flow of argon would be observed scale reading
times 0.622.
STEAM
Series PVF and CPF flowmeters may be used for vapors such
as steam. The conversion factor may be determined with the
following formula:
Where:
Mfh = Actual flow, lbs/hr.
Qm = Meter scale reading, standard.
(SCFM Dry Air @ 100 psig, 70°F.)
Sv = Specific volume of media (from steam tables)
EXAMPLE: When using a standard Series PVF and CPF gas
meter scaled for SCFM Dry Air @ 100 psig, 70°F., what is the
conversion factor for lbs/hr. steam at 50 psig, 300°F.?
Thus, actual flow of steam in lbs/hr. would be the observed scale
reading times 2.267.
5.879
6.727
Mfh = 1 x
STARTUP
System flow should be started with the by-pass valve open and
meter inlet and outlet valves closed. After the system is
operating, open the meter inlet valve gradually to equalize
internal pressure. Then slowly crack meter outlet valve and wait
for float to stabilize. Finally, slowly open the meter outlet and/or
flow regulating valve all the way and close the system by-pass
valve. AVOID SUDDEN SURGES THAT CAUSE THE METER
FLOAT TO SLAM INTO THE TOP OF THE SIGHT TUBE!
Although not essential, the meter sight tube should be filled to a
level above the float on liquid systems. The snorkel tube
(present in most standard models) allows escape of entrapped
gases except for a small pocket in the upper end which helps
cushion hydraulic shock. To assure proper filling and to flush
any foreign particles from the meter, operate the system at full
flow briefly at startup.
READING FLOW
On transparent sight tube models, read flow directly from the
scale as the number nearest the top edge of the float indicator
disk. For magnetically-linked models, flow is read at the center
of the ball indicator.
COMPENSATING FOR SYSTEM CHANGES
To find the correct flow reading for a system whose fluid
conditions vary from those for which the meter is scaled, use the
conversion data below. The most practical method of applying
the formulae is to calculate a conversion factor for the new
system conditions, multiplying the scale reading by that factor. In
the problems below, “Qs” has been assigned a value of “1” to
determine the conversion factor. (The factory can provide
special scales at additional cost for other fluids and/or units.)
CAUTION:
DO NOT OPERATE THE FLOWMETER ON A SYSTEM
EXCEEDING THE OPERATING LIMITS OF THE UNIT. WHEN
CHANGING OPERATING CONDITIONS, MAKE SURE THAT
THE NEW SYSTEM CONDITIONS ARE WITHIN THE
FLOWMETER OPERATING LIMITS, AND ALL WETTED
MATERIALS ARE COMPATIBLE WITH THE FLUID.
CORRECTING READINGS FOR NEW LIQUID CONDITIONS
Qa = Qs or Qa = Qs
Where:
Qa = Actual flow, GPM (or same units as scale).
Qs = Meter reading from scale, (scale units).
ps = Specific gravity of calibration liquid related to water in
std. atmosphere at 70° F. being 1.00.
pa = Specific gravity of metered liquid, same base.
ds = Density of calibration liquid, lbs/ft3.
da = Density of metered liquid, lbs/ft3.
pf = Specific gravity of meter float.
df = Density of the meter float per table.
ps (pf - pa)
pa (pf - ps) ds (df - da)
da (df - ds)
F-23:TEMPLATE 10/27/09 4:07 PM Page 4