Dwyer VFC Manual

Series VFC Visi-Float® Flowmeter

[266.70]

2 NOM

Specications - Installation and Operating Instructions

Bulletin F-48

Back connections

The Series VFC Visi-Float® Flowmeter is available in two basic styles, either back or
end connected with direct reading scales for air or water. Installation, operation, and
maintenance are simple and require only a few common sense precautions to assure
long, accurate, trouble-free service.

CALIBRATION

All owmeters are calibrated at the factory and normally will remain within their accuracy

tolerance for the life of the device. If at any time you wish to re-check its calibration, do

so only with instruments or equipment of certied accuracy. Do not attempt to check

the Visi-Float® owmeter with a similar owmeter as even minor variations in piping

and back pressure can cause signicant differences between the indicated and actual
readings. If in doubt, your owmeter may be returned to the factory and checked for

conformance at no charge.

LOCATION

Select a location where the owmeter can be easily read and where the temperature
will not exceed 120°F (49°C). The mounting surface and piping to the owmeter should
be free from vibration which could cause fatigue of ttings or mounting inserts. Piping
must be carefully arranged and installed to avoid placing stress on ttings and/or
owmeter body. Avoid locations or applications with strong chlorine atmospheres or
solvents such as benzene, acetone, carbon tetrachloride,etc. Damage due to contact

with incompatible gases or liquids is not covered by warranty. Compatibility should be
carefully determined before placing in service.

1-1/2

[38.10]

[50.80]

1-1/8

[28.58]

8-1/2

[215.90]

1-1/32
[26.19]

1-3/4

[44.45]

[279.40]

CONNECTIONS

4-1/2

3

1-1/2 HEX

[38.10]

11

WITH
BACK

1-1/2

[38.10]

1-1/8

[28.58]

10-1/2

[114.30]

[76.20]

1-1/2

[38.10]

SPECIFICATIONS
Service: Compatible gases and liquids.
Wetted Materials: Body: Acrylic plastic; O-ring: Buna-N (Flouroelastomer

available); Metal parts: SS; Float: SS; Fittings: VFC: PVC; VFCII: Acetal

thermoplastic.

Temperature and Pressure Limits: 100 psig (6.9 bar) @ 120°F (48°C).
Accuracy: 2% of FS.
Process Connection: VFC: 1˝ female NPT back connections.

End connections optional. VFCII: 1˝ male NPT back connections. End connections

optional.

Scale Length: 5˝ typical length.
Mounting Orientation: Mount in vertical position.
Weight: 24-25 oz (.68-.71 kg).

PIPING
Inlet Piping:

It is good practice to approach the owmeter inlet with as few elbows, restrictions and
size changes as possible. Inlet piping should be as close to the owmeter connection

size as practical to avoid turbulence which can occur with drastic size changes. The

length of inlet piping has little effect on normal pressure fed owmeters. For vacuum

service, the inlet piping should be as short and open as possible to allow operation at
or near atmospheric pressure and maintain the accuracy of the device. Note that for

vacuum service, any ow control valve used must be installed on the discharge side
of the owmeter.

DWYER INSTRUMENTS, INC.

P.O. BOX 373 • MICHIGAN CITY, INDIANA 46360, U.S.A.

Phone: [phone]

Fax: [phone]

www.dwyer-inst.com

e-mail: [e-mail]

Discharge Piping

Piping on the discharge side should be at least as large as the owmeter connection.
For pressure fed owmeters on air or gas service, the piping should be as short and

open as possible. This allows operation at or near atmospheric pressure and assures

the accuracy of the device. This is less important on water or liquid owmeters since
the owing medium is generally incompressible and back pressure will not affect the

calibration of the instrument.

POSITION AND MOUNTING

All Visi-Float® owmeters must be installed in a vertical position with the inlet
connection at the bottom and outlet at the top.

Surface Mounting

Drill three holes in panel using dimensions shown in drawing. Holes should be large

enough to accommodate #10 - 32 machine screws. If back connected model, drill two

additional holes for clearance of ttings. Install mounting screws of appropriate length
from rear. Mounting screws must not be longer than the panel thickness plus 3/8˝

(9.66 mm), or the screw will hit the plastic and may damage the meter. The screws
will require additional force during the initial installation, since the insert boots are of a
collapsed thread type and must be expanded into the plastic for the knurled surface to

take hold. Insert boots will not have the proper 10-32 threads until the rst screw has
been inserted to expand the boot. Use pipe thread sealant tape or pipe thread sealant

to insure against leakage.

CAUTION

tighten only.

In Line Mounting

Both end connected and back connected models may be installed in-line supported

only by the piping. Be sure that owmeter is in a vertical position and that piping does
not create excess stress or loading on the owmeter ttings.

Do not overtighten ttings or piping into ttings. Maximum
recommended torque is 10 ft. (lbs) (13.56 newton (meter)). Hand

MAINTENANCE

The only maintenance normally required is occasional cleaning to assure proper

operation and good oat visibility.

Disassembly

The owmeter can be completely disassembled by removing the connection ttings
and top plug. When lifting out the oat guide assembly, be careful not to lose the short
pieces of plastic tubing on each end of the guide rod which serve as oat stops.

Cleaning

The owmeter body and all other parts can be cleaned by washing in a mild soap and
water solution. A soft bristle bottle brush will simplify cleaning of the ow tube. Avoid

benzene, acetone, carbon tetrachloride, gasoline, alkaline detergents, caustic soda,
liquid soaps, (which may contain chlorinated solvents), etc., and avoid prolonged
immersion.

Re-assembly

Install the lower tting and then the oat and oat guide. Finally install the upper tting
and plug being certain that both ends of the oat guide are properly engaged and the
oat is correctly oriented. A light coating of silicone stop cock grease or petroleum jelly

on the O-rings will help maintain a good seal as well as ease assembly.

ADDITIONAL INFORMATION

For additional owmeter application information, conversion curves, correction
factors and other data covering the entire line of owmeters, please request a Dwyer

Instruments, Inc. full-line catalog.

OPERATION

Once all connections are complete, introduce ow as slowly as possible to avoid

possible damage. With liquids, make sure all air has been purged before taking

readings. Once the oat has stabilized, read ow rate by sighting across the largest
diameter of the oat to the scale graduations on the face of the device.

The standard technique for reading a Variable Area Flowmeter is to locate the highest

point of greatest diameter on the oat, and then align that with the theoretical center
of the scale graduation. In the event that the oat is not aligned with a grad, an
extrapolation of the oat location must be made by the operator as to its location
between the two closest grads. The following are some sample oats shown with
reference to the proper location to read the oat.

Variable Area Flowmeters used for gases are typically labeled with the prex “S” or
“N”, which represents “Standard” for English units or “Normal” for metric units. Use
of this prex designates that the owmeter is calibrated to operate at a specic set of

conditions, and deviation from those standard conditions will require correction for the

calibration to be valid. In practice, the reading taken from the owmeter scale must

be corrected back to standard conditions to be used with the scale units. The correct

location to measure the actual pressure and temperature is at the exit of the owmeter,
except under vacuum applications where they should be measured at the owmeter

inlet. The equation to correct for nonstandard operating conditions is as follows:

Q2 = Q1 x

Where: Q1 = Actual or Observed Flowmeter Reading
Q2 = Standard Flow Corrected for Pressure and Temperature

P1 = Actual Pressure (14.7 psia + gage pressure)
P2 = Standard Pressure (14.7 psia, which is 0 psig)

T1 = Actual Temperature (460 R + Temp °F)
T2 = Standard Temperature (530 R, which is 70°F)

P1 x T2
P2 x T1

Example: A owmeter with a scale of 10-100 SCFH Air. The oat is sitting at the 60
grad on the owmeter scale. Actual Pressure is measured at the exit of the meter as 5

psig. Actual Temperature is measured at the exit of the meter as 85°F.

Q2 = 60.0 x

Q2 = 68.5 SCFH Air

(14.7 + 5) x 530

14.7 x (460 + 85)

Printed in U.S.A. 6/20 FR# 440448-00 Rev. 5©Copyright 2020 Dwyer Instruments, Inc.

DWYER INSTRUMENTS, INC.

P.O. BOX 373 • MICHIGAN CITY, INDIANA 46360, U.S.A.

Phone: [phone]

Fax: [phone]

www.dwyer-inst.com

e-mail: [e-mail]