McCrometer V-Cone Troubleshooting Manual

V-Cone Troubleshooting Guide

Company name: McCrometer Inc.

Address: 3255 W. Stetson Ave.

Hemet, California, USA 92545-7799

General office phone: [phone]

Facsimile : [phone]

E-mail: [e-mail]

Internet: www.mccrometer.com

Troubleshooting a V-Cone System On-Site

This guide is intended to help you troubleshoot a V-Cone system. Keep several points in
mind as you proceed:

1. Most V-Cones are calibrated devices. The meter has already had flow through it. If a

cone is missing or a leak exists inside the meter, this would be discovered during the
calibration.

2. A flow measurement requires a system. Do not assume a problem exists with the

primary element just because it is called a V-Cone system. Most problems occur in
the DP transmitter or the flow computer.

3. This guide assumes a simple system of meter, manifold, DP transmitter, and flow

computer. Systems can be much more complex with pressure and temperature
transmitters, as well as full scale digital control systems. Do not limit your evaluation
to just these suggestions.

4. If you discover a problem / solution not listed in this guide, please let Stephen Ifft at

McCrometer know at 1-909-765-5344 or [e-mail].

This guide separates the flow measurement system into areas. These areas are labeled in
the diagram below:

V-Cone

Manifold Transmitter

Gauge lines

Flow computer

During troubleshooting, make a preliminary assessment of the symptoms of the problem
and consult the following chart.

 1999 by McCrometer/Printed in U.S.A. 2-99/Lit #: 24509-90 Rev 1.0

Page 1 of 5

SYMPTOM AREA

No signal
(0 mA)

Negative signal

Transmitter
Transmitter

Transmitter
(< 0 mA)
Low signal

V-Cone
(<4 mA)

Gauge

lines

Transmitter

Zero signal
(4 mA)

V-Cone

V-Cone

Manifold

Transmitter

Wrong signal –

V-Cone
high or low

V-Cone

Gauge

lines

Flow

computer

Flow

computer

POSSIBLE PROBLEM / SOLUTION

No power to transmitter.
Transmitter not wired correctly. Perform continuity check on wiring.
Transmitter wires are reversed.

V-Cone installed backwards, with gauge lines attached as marked. In this
case, the high pressure tap would be sensing a lower pressure than the low
pressure tap. This negative DP would force the signal below 4 mA.
Gauge lines are reversed. Transmitter sees more pressure on low side than
high side. Check “H” and “L” marks on V-Cone and transmitter.

Transmitter is malfunctioning. Some transmitters will send a specified
mA signal when a malfunction occurs. This can be set to low values, such
as 3.8 mA, or high values, such as 20.1 mA.
Meter has been damaged. Remove meter and visually inspect.

No flow in pipeline. Check other system locations to verify flow through
the meter. The meter could be under pressure but still have no flow.
Manifold / gauge lines closed or blocked. Ensure valves and lines are
open. If fluid is safe, open vent valves on transmitter to verify pressure in
the gauge lines.
Transmitter is check mode. Some transmitters allow for system checks by
forcing the signal to 4 or 20 mA. Vent low side of transmitter to ensure
the signal responds to pressure changes.
Process conditions do not match actual conditions. Contact McCrometer
or your sales representative to recalculate using the correct process
conditions.
Wrong meter. Verify serial numbers on meters to ensure correct
specifications. Sometimes two meters are interchanged. Remember each
V-Cone has a unique flow coefficient.
Foreign material trapped in gauge lines. Dirt and sediment can settle into
the gauge lines. If the fluid is safe, vent the gauge lines and inspect for
spurts of solids, gasses, or liquids (whichever should not be there). If the
fluid is not safe, open the center manifold valve for several minutes under
high DP. Close the valve and compare the signal level to before. In a
horizontal, liquid application, install the meter with the taps on the sides of
the pipe (3 or 9 o’clock) For a horizontal, gas application, install at top or
sides of the pipe (12, 3, or 9 o’clock).
Flow calculations are in error. Use loop calibrator and apply 4, 12, and 20
mA to computer / system. Each of these points should correlate with the
V-Cone sizing information.
mA signal is read incorrectly. Apply a known current to the loop and read
the raw signal in the computer. Most computers allow the user to see the
mA signal directly.

 1999 by McCrometer/Printed in U.S.A. 2-99/Lit #: 24509-90 Rev 1.0

Page 2 of 5

Signal too high

V-Cone

V-Cone

V-Cone

V-Cone

Gauge

lines

Transmitter

Transmitter

Transmitter

Transmitter

/ flow

computer

Flow

computer

V-Cone is installed backwards. Look for a flow direction arrow on the
meter body, near the pressure taps. If no arrow is visible and the meter is
large than 2 inches, the flow direction can be determined by the location
of the pressure taps. The pressure taps will be closer to the upstream side.
On meters less than 2 inches, the gauge lines will need to be removed.
Look at the base of both pressure taps. One tap will be smooth at the base,
the other will be mostly weld material. The smooth tap is on the upstream
side. With a meter measuring backward flow, the DP signal will be
approximately 30% too high.
Flow is going in opposite direction as expected. The assumption of flow
direction is sometimes wrong. Verify with other system readings. With a
meter measuring backward flow, the DP signal will be approximately 30%
too high.
Partially full pipe (liquids only). A partially full pipe will cause the meter
to read too high. This can happen even in pressurized systems.

• On horizontal pipes: If the fluid is safe, open a pressure tap on the top

of the pipe. Air release will indicate partially full pipe.

• On vertical pipes: Up flow will guarantee a full pipe. Down flow is

difficult to diagnose if the pipe is full.
Foreign object lodged in meter. This will increase the restriction of the
meter and raise the DP. Remove the meter and visually inspect.
Leak on low pressure gauge line. Perform a leak check from the meter to
the transmitter.

Leak on low pressure vent valve. Perform a leak check on valve.
Zero point has shifted positively. This will cause errors more pronounced

at the low end of the transmitter range. Verify by closing the manifold side
valves and opening the center valve. The reading should go to zero (4
mA). Recalibrate if necessary.
DP span is set too low. Use pressure calibrator or handheld communicator
to verify span point.
Both the transmitter and flow computer are set to take the square root of
the signal. The signal will be correct at 20 mA. The positive error will
increase dramatically as the signal decreases from 20 mA. Use a loop
calibrator to check 12 mA point.
4 mA set to minimum flow. Our calculations assume that 4 mA will be
equal to zero flow. Sometimes 4 mA is set to equal the minimum flow on
the sizing page. This error will be zero at maximum flow and increase as
the flow decreases. The amount of error will depend on the zero offset.

 1999 by McCrometer/Printed in U.S.A. 2-99/Lit #: 24509-90 Rev 1.0

Page 3 of 5

Signal too low

Unsteady signal

Slow response
time
Sudden change
in readings

Manifold

Gauge
lines
Transmitter
Transmitter

Transmitter
Transmitter

/ flow
computer

V-Cone
Transmitter
Transmitter

V-Cone
Gauge

lines

Manifold is cross-vented. The center valve must be closed. To test, close
the two side valves and watch the transmitter signal. If the signal goes to
zero (4 ma), the center valve is not closed completely.
Leak on high pressure gauge line. Perform a leak check from the meter to
the transmitter.

Leak on high pressure vent valve. Perform a leak check on valve.
Zero point has shifted negatively. This will cause errors more pronounced

at the low end of the transmitter range. Verify by closing the manifold side
valves and opening the center valve. The reading should go to zero (4
mA). Recalibrate if necessary.
DP span is set too high. Use pressure calibrator or handheld
communicator to verify span point.
Neither the transmitter nor flow computer is set to take the square root of
the signal. The signal will be correct at 20 mA. The negative error will
increase dramatically as the signal decreases from 20 mA. Use a loop
calibrator to check 12 mA point.
Partially full pipe occurring (liquids only). Periods with a partially full
pipe will cause erratic readings. See above for details.
Power supply not supplying enough power to create signal. Check power
specifications for transmitter.
Dampening.

Foreign object lodged in meter. This will increase the restriction of the
meter and raise the DP. Remove the meter and visually inspect.
Leaks have started.

 1999 by McCrometer/Printed in U.S.A. 2-99/Lit #: 24509-90 Rev 1.0

Page 4 of 5

Recommended Equipment for

Troubleshooting a V-Cone Installation On-Site:

1. 4 to 20 mA loop simulator – highly recommended

2. Digital multimeter: with VDC, I, and Ω measurements

3. Pressure calibrator

4. Handheld Communicator for smart instruments

5. Hand tools: Screwdriver(+), Screwdriver (–), 12 inch crescent wrench, 4

inch crescent wrench

Some suggestions for equipment manufacturers and their products follow. A wide range
of products is available. We do not necessarily endorse these products or companies.
Please choose a product that fits your needs and resources.

www.fluke.com

740 Series Documenting Process Calibrators
718 Pressure Calibrator
717 30G Pressure Calibrator
716 Pressure Calibrator
715 Volt/mA Calibrator
714 Thermocouple Calibrator
713 30G/100G Pressure Calibrator
712 RTD Calibrator
787 Process Meter (combination digital multimeter and loop calibrator)
705 Loop Calibrator

 1999 by McCrometer/Printed in U.S.A. 2-99/Lit #: 24509-90 Rev 1.0

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