Dwyer VFB User Manual

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Series VF Visi-Float

®

Flowmeter

Specifications - Installation and Operating Instructions

Fig. 1

Model VFB Model VFA-SSV

The Visi-Float® Series Flowmeters are furnished in two models (see

Figure 1) each available in a broad choice of flow ranges with direct
reading scales for air, gas or water. Installation, operation and
maintenance are very simple and only a few common sense precautions
must be observed to assure long, trouble-free service.

CALIBRATION

Each flowmeter is calibrated at the factory. If at any time during the
meter’s life, you wish to recheck its calibration, do so only with devices
of certified accuracy. DO NOT attempt to check the Visi-Float
Flowmeter with a similar flowmeter as seemingly unimportant variations
in piping and back pressure may cause noticeable differences in the
indicated reading. If in doubt, return your flowmeter to the factory. It will
be checked for conformance at no charge. Before proceeding with the
installation of your Visi-Float®Flowmeter, check to be sure you have the
model and flow range you require.

LOCATION
Temperature, Pressure, Atmosphere, and Vibration:

Visi-Float® Acrylic Flowmeters are exceptionally tough and strong. They
are designed for use at pressures up to 100 psi (7 bar) and
temperatures up to 150°F (66°C). DO NOT EXCEED THESE LIMITS!
The installation should not be exposed to strong chlorine atmospheres
or solvents such as benzene, acetone, carbon tetrachloride, etc. The
mounting panel should be free of excessive vibration since it may
prevent the unit from operating properly.

Inlet Piping Run: It is good practice to approach the flowmeter inlet with
as few elbows and restrictions as possible. In every case the inlet piping
should be at least as large as the connection to the flowmeter i.e.
Pipe Size. Length of inlet piping makes little difference for normal
pressure fed flowmeters.

For flow meters on vacuum air service the inlet piping should be as short
and open as possible. This will allow operation near atmospheric
pressure and thereby insure the accuracy of the device. (Note that for
vacuum air service the flow control valve if any, should be on the
discharge side of the flowmeter. Either the TMV unit or a separate in line
valve may be applied.)

Discharge Piping: As on the inlet, discharge piping should be at least
as large as the flowmeter connection. In addition, for pressure fed
flowmeters on air or gas service the discharge piping should be as short
and open as possible. This will allow operation of the flow tube at near
atmospheric pressure and insure the accuracy of the device. This is of
less importance on water or liquid flowmeters since the flowing medium
is generally incompressible and moderate back pressure will not affect
the accuracy of the instrument as calibrated.

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/8˝ Iron

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*VFB ranges 85 and 86 have 1/4˝ NPT back connections or 3/8˝ NPT end connections.

SPECIFICATIONS
Service: Compatible gases & liquids.
Wetted Materials:

Body: Acrylic plastic.
O-ring: Buna-N (Fluoroelastomer available).
Metal Parts: Brass standard, SS optional.
Float: SS, black glass, aluminum, K Monel depending on range.

Temperature & Pressure Limits:

Without Valve: 100 psig (6.9 bar) @ 150°F (65°C);

With Valve: 100 psig (6.9 bar) @ 120°F (48°C).

Accuracy: VFA = 5% FS; VFB= 3% FS.
Process Connection: 1/8˝ female NPT. VFB ranges 85 and 86 have

1/4˝ NPT back connections or 3/8˝ NPT end connections. These ranges
not available with brass valves.

Scale Length: VFA 2˝ typical length; VFB 4˝ typical length.
Mounting Orientation: Mount in vertical position.
Weight: VFA: 4.0-4.8 oz (.11-.14 kg). VFB: 7.2-8.8 oz (.20-.25 kg).

POSITION AND MOUNTING

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

Surface Mounting: Drill appropriate holes in panel using the dimensions
shown in Figure 1. Hold the flowmeter in position in front of the panel and
install the mounting screws through the panel from the rear. Mounting
screws must not be longer than the panel thickness plus 1/4˝, 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

DWYER INSTRUMENTS, INC.

P.O. BOX 373 • MICHIGAN CITY, IN 46360, U.S.A. Fax: [phone] e-mail: [e-mail]

proper 10-32 threads until the first screw has been inserted to expand

Phone: [phone] www.dwyer-inst.com

IMENSION-IN INCHES

D

Model VFA

4

3 (1/8 female NPT)

1-5/8 (10-32 Thread)

1/2

1-3/16

1-1/4

2-1/16 (BV or SSV)

4-3/32

1

3/4 (EC)

3/32 (EC)

Model VFB

5-1/2 (1/8female NPT)*

3-1/2 (10-32 thread)

2-1/16 (BV or SSV)

150 psig (10 bar) @ 100°F (38°C).

6-1/2

1/2

1-1/2
1-1/4

6-19/32

1-3/8

3/4 (EC)

3/32 (EC)

POPULAR RANGES

Model VFA — 2" Scale

Range

No.

1
2
3
4
5
6
7
8
9

2

3
33
34

Range

SCFH Air

.1-1
.2-2
.6-5

-10

1

-20

2
4-30

-50

5
0-100

1

0-200

2

C Water

C

er min.

p

-50

6
0-100

1
20-200

R

ange

o.

N

21

2

2
23
24
25
26
27

1

4

2

4

3

4

4

4

Range

LPM Air

.06-0.5

.15-1

.6-5

-10

1

-25

3

-50

6
0-100

1

al. Water

G

er hour

p

6-5

.

1.2-10
3-20
8-40

Model VFB — 4" Scale

R

ange

o.

N

0

5

1

9

1

5
52

3

5
54

5

5

90

0

6

Range

SCFH Air

.3-3
1-10
2-20
4-40
0-100

1
15-150
20-200

SCFM Air

3-3

.

CC/Min. Air

00-1000

1

Range

No.

65
66
67
68
69

82

80

3

8
81

85
86

LPM Air

.2-4

1-10

-20

1
3-30
4-40

C/Min. Water

C

2-30

PH Water

G

.5-12

1-20
6-60

GPM Water

.2-2
.5-5

the boot. Pipe up inlet and discharge using pipe thread sealant tape or
pipe thread sealant to insure against leakage.

Surface Mounting on Piping Only: An alternate method of surface
mounting is by omitting the mounting screws and supporting the Visi­Float®Flowmeter on the connecting piping only. For this method extra
long or straight pipe threads should be used so that nuts may be run onto
the pipe and later tightened against the back of the panel to retain the
unit in proper position. Use the appropriate hole layout information from
Figure 1, but omit the small holes.

Mounting on Piping Only Without Panel: For the temporary or
laboratory type installation, the panel may be omitted altogether and the
flowmeter installed directly in rigid piping. Its light weight permits this
without difficulty.

OPERATION

To start system, open the valve slowly to avoid possible damage. Control
valves on BV and SSV models are turned clockwise to reduce flow,
counter clockwise to increase flow (valve is designed for flow adjustment
only, not intended to be used as an open/shut-off valve). A nylon insert is
provided in the threaded section of the valve stem to give a firm touch to
the valve and to prevent change of setting due to vibration.

The performance of low range units used in air or gas applications may
be affected by static electricity. Excessive static charge may cause the
ball float to behave erratically or provide a false reading. To ensure the
proper function of the unit, the application should be designed to
minimize or dispel static electricity.

The standard technique for reading a Variable Area Flowmeter is to
locate the highest point of greatest diameter on the float, and then align
that with the theoretical center of the scale graduation. In the event that
the float is not aligned with a grad, an extrapolation of the float location
must be made by the operator as to its location between the two closest
grads. The following are some sample floats shown with reference to the
proper location to read the float.

CAUTION

Do not completely unscrew valve stem unless flowmeter is
unpressurized and drained of any liquid. Removal while in service
will allow gas or liquid to flow out front of valve body and could
result in serious personal injury. For applications involving high
pressure and/or toxic gases or fluids, special non-removable
valves are available on special order. Contact factory for details.

Variable Area Flowmeters used for gases are typically labeled with the
prefix “S” or “N”, which represents “Standard” for English units or
“Normal” for metric units. Use of this prefix designates that the flowmeter
is calibrated to operate at a specific 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 flowmeter 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 flowmeter, except under vacuum applications where
they should be measured at the flowmeter inlet. The equation to correct
for nonstandard operating conditions is as follows:

Q2= Q1x P1x T

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)

Example: A flowmeter with a scale of 10-100 SCFH Air. The float is sitting
at the 60 grad on the flowmeter 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 (14.7 + 5) x 530

Q2= 68.5 SCFH Air

MAINTENANCE

The only maintenance normally required is occasional cleaning to assure
reliable operation and good float visibility.

Disassembly: The flowmeter can be disassembled for cleaning by
simply disconnecting the piping, dismounting the unit from the panel and
removing the top-plug-ball stop. Take out the ball or float by inverting the
body and allowing the float to fall into your hand. (Note: It is best to cover
the discharge port to avoid losing the float through that opening.) When
removing the float guide assembly on VFB models 85 and 86, be careful
not to lose the short pieces of plastic tubing on both ends of the guide
which serve as float stops.

Cleaning: The flow tube and flowmeter body can best be cleaned with a
little pure soap and water. Use of a bottle brush or other soft brush will
aid the cleaning. Avoid benzene, acetone, carbon tetrachloride, alkaline
detergents, caustic soda, liquid soaps (which may contain chlorinated
solvents), etc. and avoid prolonged immersion.

Reassembly: Reinstall the float, remount, connect and place the unit
back in service. A little stop cock grease or petroleum jelly on the “O”rings
will help maintain a good seal as well as facilitate assembly. No other
special care is required.

For VFB models 85 and 86, first install the lower fitting, next the float
guide and float and finally the upper fitting and plug. Be certain that both
ends of the float guide are properly engaged and the float is correctly
oriented.

ADDITIONAL INFORMATION

For additional flowmeter application information, conversion curves,
factors and other data covering the entire line of Dwyer Instruments, Inc.
full-line catalog.

2

1

P2x T

14.7 x (460 + 85)

©Copyright 2013 Dwyer Instruments, Inc. Printed in U.S.A. 6/13 FR# 52-440241-00 Rev.6

DWYER INSTRUMENTS, INC.

Phone: [phone] www.dwyer-inst.com

P.O. BOX 373 • MICHIGAN CITY, IN 46360, U.S.A. Fax: [phone] e-mail: [e-mail]