Verification of Fuel Dispensing Pumps

Part IV of Eighth Schedule, The Legal Metrology (General) Rules, 2011

Specific provision: Part 2 Rule 5(1)

A dispensing pump is a measuring instrument used in conjunction with a storage tank for effecting delivery of liquid products by specified volume. The instrument should be able to measure continuously, memorize and display the volume of liquid passing through the measurement transducer.

A fuel-dispensing system contains several sets of components to perform a number of interrelated functions. Some components maintain hydraulic continuity; regulate the direction of flow and fluid pressure. Others put the pressure on the fuel to move it through the system. Some other components are responsible for metering the liquid fuel, registering accurately the quantity delivered, and computing the price of the delivery. These components are subject to metrological control. Another set of components control the operation of the system, switch it on and off, resets the volume and price indicators, and regulates the delivery. Resetting of indicators and delivery regulating components are also subject to metrological control.

Hydraulic part of a dispenser

When a dispenser is switched on, the electric motor is activated, and begins draw fuel from its outlet. This displacement of the liquid creates a partial vacuum at the pump inlet. When the discharge nozzle remains closed, the vacuum is relieved by fuel circulating continuously through the unit. But when the nozzle is opened, suction pressure is transferred instantaneously from the pump inlet to the storage tank through the pipe line. There, atmospheric pressure forces the fuel to flow through a check valve toward the dispenser.

Before entering the pumping unit, it passes through a strainer or filter, which removes any solid particles. Small quantities of trapped air and fuel vapor are also removed from the fuel through an air separator chamber.

Then the fuel, free of air and vapor, passes to the automatic control valve which permits fuel to flow only in the direction of the meter, never back to the pump. Now-a-days, the control valve is replaced by a solenoid and pilot valve.

The Metering and the Registering part

Working principle of mechanical and semi mechanical units

While the hydraulic part of a dispensing unit will remain more or less similar, working principle of the metering and registering part of mechanical, semi-mechanical (Z types for example) and electronic units are totally different. Requirement for sealing of those units will also be different.

Metering part for both the types are similar. But, mechanical dispensers employ mechanical registering unit of analog display while a semi-mechanical dispenser uses a digital display unit. In the former type the metering unit is connected to the registering unit through a gear box while in the later type a sensor (a device which transforms mechanical force into electronic signals) is used for the connection

Metering Unit

The main components are the Adjustment wheel by which the delivery is controlled (calibration), the Cylinders and the Gear Box.

Metering devices mostly use piston meters and are positive-displacement. A piston moving through a cylinder filled with liquid will displace a quantity of liquid which will be determined by the bore of the cylinder and the stroke of the piston. Usually four cylinders are used. The pistons operate may operate in a horizontal plane or in a vertical plane and convert their to reciprocating action to a rotary shaft output to drive either a sensor or a mechanical computer (gear box).

The metering units are calibrated at the factory. Normally, the calibration is of high accuracy and reliable. However, meters may need adjustment after period of usage or deliberate mal-adjustment to cross the MPE limit.

These adjustments can be made in very small quantity as little as 3/10,000 part of volume. The adjusting mechanism may be located on the top of the meter or on one of the piston caps. It may be a knurled knob, keyed disk, or calibrated wheel or have some other but immediately identifiable design. The disc or wheel or any other adjusting device must have locking pins or fixed perforated screws for sealing.

Inside and outside of two common types of gear box

Gear boxes and adjustment wheels are major components which are manipulated mostly by unscrupulous dealers.

Extra precaution is required for sealing the Gear Box and the Adjustment wheel. All the three components are sealed individually with one long multi threaded wire.

The Registering Unit

The rotary shaft output of the metering unit drives a registering unit, which may be old fashioned mechanical computer, or a sensor or pulser in electrical installations.

In mechanical registers the display is analog. It has two panels of computing and display. The lower panel indicates the volume delivered with 1/10th divisions of a litre, in an operation. The display has to be reset to zero before the next operation can begin. The upper panel, known as totalizer, registers the total volume dispensed by the unit. The indication must be irreversible and is sealed to prevent any change in display.

Such registering units are still found in small towns and mainly in the rural areas

In semi-mechanical registering units, a sensor is used to convert the mechanical energy og the meter shaft to convert it into electrical signal. The output of the sensor is sent to the digital display panel. The panel shows both the volume displayed in an opration and also the total volume dispensed by the unit. Here again, the volume indicator is set to zero before the next operation can begin and the totalizer is ir-reversible. The sensor box is need to be sealed to prevent any unauthorized adjustment.

Such type of units are found in semi-urban or rural areas and are known as Z-series pumps because of their design.


Working Principle of Electronic Multiple Product Dispensers

Electronic Multiple Product Dispensers (MPD) devices used for measuring and transferring a specified volume of a number of liquid fuels from a single equipment.
Apart from the introduction of solenoid valve, which is controlled by the micro-processor, rest of the hydraulic section is more or less the same as those in older mechanical units.

The electronic Device

The heart of the system is the Central Processing Unit (CPU), a micro-processor with an in-built memory chip. It controls the entire set of measuring, display, delivery and associated devices of preset keypad, receipt printer etc.

An MPD, being an electronic device uses a transducer, generally called a pulser, which is coupled directly to the meter shaft. The pulser converts the mechanical force of the rotating shaft into discreet electrical pulses. These pulses are transmitted as input to the CPU. The CPU recognizes not only pulse signals but electrical signals from other input devise - zero reset, price adjustment, preset mechanism etc. After all the information are processed, the CPU sends appropriate signal to the display panel (through the display card), to the printer, if connected and also to the solenoid valve to control rate of flow of liquid through the meter. The rate increases in the beginning, remains steady in the middle and slows down towards the end of delivery.

The pre-set key pad is used to transmit the pre-set the quantities or total price of fuel to be delivered and also credit card details.

The display panel normal bears the following information - price per litre, quantity delivered and price. There is also a totalizer to register total quantity of fuel deliver from the unit.

Upper Chamber

The Upper Chamber holds the electronic part of the unit. It contains the main mother board of the processor along with memory chip, connected to all input devices and output devices. The all important DIP switch Box, also known as Black Box, used for electronic calibration, is located here. Other major components are Calibration Card, Display Card and Unit and Totalizer. Calculating device - Preset Keyboard and Printing Device are also connected to the mother board.

Components of this chamber which require sealing are - Dip Switch Box, Display Unit and the Totalizer.

In a chamber there may be as many as four units, two in each side, one unit each for 4 types of fuels - High Speed Diesel, Super Diesel, Un-leaded Petrol and normal Petrol.

Functioning of the Calibration Card

Calibration means the process of adjusting the calibration mechanism of a measuring instrument so that it functions within its standard accuracy.

In an MPD or an electronic device,Calibration Card is the most important component of the system system because it controls the actual quantity of fuel supplied to the nozzle. On the card, there is a black box inside which the Dual In-line Package (DIP) Switch is placed. This switch is required to be set ON for calibrating the pump for correct delivery. Naturally, this box needs additional protection. After, switching on the DIP, the calibration is made through the preset calculator through a series of commands, as may be given in the user manual.
However, the limit of adjustment through the calibrating card is ±150 ml in 5 l. Change in delivery beyond that is possible through rotating the adjustment gear or turning the adjustment rod inside the meter.

Electronic Calibration

  • The DIP Switch Box on the PCB (Printed Circuit Board), or somewhere near, is opened and switched on.
  • Enter calibration mode using a code number.
  • Enter user PIN.
  • Calibrate for 5 l or 20 l. (The calibration can change delivery up to ±150 ml in 5 l.)

Manual Calibration

When the calibration cannot be made up to a desired level by electronic method, manual calibration is done. This is done though calibrating the meter either by< rotating the adjustment gear or turning the adjustment rod after lifting the adjustment knob to free it from the meter shaft.

Caution

It is not enough to guard the Calibration Device through a PIN Code only. Under the provision of Rule 2(20)(ii), in an instrument meant for selling to the public, there should also be a Hard Key, a locking device. The device should be sealed so that it cannot be opened unauthorizedly.

Calibration History

The memory chip maintains a history of last ten attempts of calibration. It can be retived by typing appropriate keys of the keyboard as given in the user manual. It is very helpful to detect any attempt of unauthorized calibration. The history consists of Calibration factor of the nozzle. no of calibrations attempted and the Totalizer reading after the calibration. These figures may be noted for any future comparing.

Verification Procedure

Equipment

1. Certificate/s of model approval.
2. Appropriate working standards of measurement as
(a) A volume measure of at least 10 L capacity suitable for deliveries at maximum flow rate specified for the dispenser. The measure should be suitable for deliveries greater than three times the minimum measured quantity (Vmin) specified for the dispenser. For dispensers greater than 60 L/min use a measure with a volume equivalent to at least 1 min delivery for both maximum and minimum flow rate.
(b) A small capacity measure verified at relevant intervals for tests where small measures are required.

Preparation

The first fill into a dry standard volume measure may produce erroneous results if the internal walls of the measure are not wet with the liquid to be measured. Hence, it is essential that all working standard volume measures be conditioned (wetted and drained) before being used. This procedure is only needed on the initial test run, and is not required on subsequent deliveries as long as the measure remains conditioned.

Test Procedures

The following series of test procedures determine if the performance of a fuel dispenser meets requirements and whether the dispenser requires adjustment or service. Each test procedure is explained as a discrete test. However tests can be combined to expedite the testing procedure.

min of 2 L.

1. Checking Facility for Electronic Indicating Devices

The checking facility for an electronic indicating device shall provide visual checking of the entire display, which shall meet the following description (Part 2, clause 4.3.iv.b):

  • displaying all the elements (eights test);
  • blanking all the elements (blank test); and
  • displaying zeros.
This test can be carried out in conjunction with the test for zero setting.

1. Remove the nozzle from its hang-up position and check that the:

  • display test is performed; and
  • display segments are not faulty.
2. Determine whether the dispenser has passed or failed.

2. Zero Setting

The zero-setting devices of the price-indicating device and of the volume-indicating device shall be designed in such a way that zeroing either indicating device automatically involves zeroing the other Part 2, clause 3.3.v)

The zero-setting device shall not permit any alteration of the measurement result shown by the price/volume-indicating device other than by making the result disappear and displaying zeros (Part 2, clause 3.2.iv. b)

Once the zeroing operation has begun it shall be impossible for the price/volume-indicating device to show a result different from that of the measurement that has just been made, until the zeroing operation has been completed. The price/volume-indicating device shall not be capable of being reset to zero during measurement (Part 2, clause 3.2.iv.c)

Determine whether zero setting is mechanical or electronic and conduct the appropriate test as follows:

2.1 Mechanical Reset Mechanism

For mechanical indicating devices, the residual volume indication after return to zero shall not be more than half the minimum specified volume deviation (Emin), e.g. 10 ml for dispensers with a Vmin of 2 L (Part 2; clause 3.2.iv.d).

Likewise, the residual price indication after return to zero shall not be more than half the minimum specified price deviation (MSPD) where MSPD = Emin X unit price (Part 2, clause 3.3..viii).

  • Remove the delivery nozzle from its hang-up position.
  • If a previous sale remains on the indicator move the starting lever to the ON position and ensure that the pump motor does not start or the dispenser is not activated. If the pump motor does start or the dispenser is activated then the inter-lock mechanism is faulty.
  • Reset the indicator/s to zero and check that the volume indicator/s is/are zero within 0.5 Emin and the price indicator/s is/are zero within Emin X unit price X 0.5.
  • Move the starting lever slowly and gently towards the ON position until the motor starts (or the dispenser is activated) and then slowly and gently towards the OFF position until the motor stops (or the dispenser is de-activated).
  • Move the starting lever slowly and gently towards the ON position and check that the interlock has engaged and prevents the motor from starting or being activated.
  • Return the starting lever to the OFF position.
  • Determine whether the dispenser has passed or failed.

2.2 Electronic Reset Mechanism

For electronic indicating devices, the price/volume indication after return to zero shall be zero without any ambiguity (Part 2, clauses 3.2.iv.e and 3.3.ix).

  • Remove the nozzle from its hang-up position and ensure that the display test is performed and the price and volume displays are on zero before any delivery of product is possible.
  • Carefully return the nozzle to its hang up position and ensure that when the nozzle is then removed no further deliveries are possible without the segment test being initiated and the indications returning to zero.
  • Determine whether the dispenser has passed or failed.

3. Price Computing

The price indicated shall equal the price calculated from the volume and unit price.

This test can be done at any time during a test delivery, e.g. accuracy test or nozzle shut off test.

  • Reset the dispenser to zero.
  • Make a delivery of a convenient volume.
  • Calculate the total price from the unit price and total volume indicated.
  • Compare this calculated price with all displays.
  • Determine whether the dispenser has passed or failed.

4. Nozzle Cut-off

Where the hose is fitted with an automatic cut-off nozzle the nozzle should close automatically when the sensing port of the nozzle comes in contact with liquid or froth.

This test can be done during accuracy or anti-drain testing.

  • Make a delivery at normal flow rate.
  • Allow the sensing port of the nozzle to come in contact with liquid or froth.
  • Ensure the nozzle cuts off.
  • Repeat steps 1 to 3 twice more.
  • Determine whether the dispenser has passed or failed.

5. Interlock

The use of the same indicating device for the indications of several measuring systems (which have a common indicating device) is authored provided it is impossible to use any two of these measuring systems simultaneously (Part 2, clause 2.9.vi).

In measuring systems intended to deliver liquids, no means shall be provided by which any measured liquid can be diverted (Part 2, clause 2.16.i).

The selected unit price shall be displayed by an indicating device before the start of the measurement (Part 2, clause 3.3.ii)

These requirements are interpreted to mean that no fuel can be dispensed unless it is measured and that the unit price indicated corresponds to the unit price of the fuel selected and delivered.

Determine whether the hoses have a common indicator or whether they share a pumping unit, and conduct the appropriate test as documented below.

5.1 Hoses Sharing a Common Indicator

  • Select and authorize one hose and remove the nozzle from its hang-up position.
  • Check that the price and volume indications for the hose selected reset to zero, and for dispensers:
    with separate unit price display:
    the unit price display for the type of fuel selected is transferred to the main indication;
    without separate unit price display:
    the unit price display for the hose selected is displayed and all other unit price displays disappear until the delivery has been completed.
  • Check that all other hoses sharing the same indicator are disabled by removing the other nozzles from their hang up position and confirming that they do not authorize.
  • Determine whether the dispenser has passed or failed.

5.2 Hoses Sharing a Pumping Unit

  • Select and authorize any hose that shares a common pumping unit.
  • While the pumping unit is operating, attempt to make a delivery from any other hose connected to the same pumping unit without allowing the indicator to reset to zero.
  • Check that it is not possible to make a delivery from any other unauthorized hose connected to the same pumping unit.
  • Determine whether the dispenser has passed or failed.

6. Pre-set Indications

Measuring systems with a price-indicating device may also be fitted with a price/volume pre-setting device, which stops the flow of the liquid when the price/quantity corresponds to the pre-set value Part 2, clause 3.6.x).

This test can be combined with the pre-set accuracy test and one result recorded.

  • Reset the dispenser to zero.
  • Enter a suitable pre-set value using the pre-set facility. Make sure the pre-set amount appears on the display.
  • Commence a delivery into the container with the nozzle fully open allowing the pre-set facility to slow down and complete the delivery automatically.
  • Check that the price/volume indication on the display corresponds to the pre-set amount and for self-serve remains on the display or is stored in memory until the transaction is finalized.
  • Determine whether the dispenser has passed or failed.

7. Maximum Flow Rate

The maximum achievable flow rate shall be within the approved range (Qmin to Qmax) marked on the data plate. This test is only indicative that the maximum achievable flow rate is within the approved range and can be performed during one of the fast flow accuracy test deliveries.

Determine whether the hoses have their own pumping unit or whether they share a pumping unit, and conduct the appropriate test as specified below.

Hoses with their own Pumping Unit

1. Commence and time a delivery at the maximum achievable flow rate.
2. Stop the delivery after at least 10 s.
3. Note the indication on the dispenser and calculate the flow rate.
4. Determine whether the dispenser has passed or failed.

Hoses Sharing a Pumping Unit

This is a requirement at initial verification/ certification, when any site changes occur, or at the discretion of the trade measurement authority. Refer to the certificate of approval for specific tests.

1. Select and authorize a number of hoses connected to the same pumping unit.
2. With all hoses operating at the maximum achievable flow rate, time the delivery for one of the hoses.
3. Stop the delivery after at least 10 s and calculate the flow rate.
4. Determine whether the dispenser has passed or failed.

8. Accuracy

It is recommended that testing be carried out at the maximum achievable flow rate and at Qmin (as per the procedure) and the results analyzed to determine if the meter requires adjustment.

1. Condition the working standard volume measure
2. Make a delivery at maximum achievable flow rate. Record the volume indicated by the fuel dispenser (VFD) and the volume indicated by the working standard measure (VREF).
3. Calculate and record the relative error (EFD).
EFD = (VFD - VREF) / VREF X 100
4. Repeat steps 2 to 3 twice more.
5. Make one more delivery at minimum flow rate. Record the volume indicated by the fuel dispenser (VFD) and the volume indicated by the working standard measure (VREF).
6. Calculate and record the relative error (EFD).
7. Determine if all the results are within the allowable MPE. If not, analyze the results and assess whether or not the meter can be adjusted so that all the results are within MPE.
8. If meter adjustments are made, circulate a quantity of fuel and repeat steps 2 to 7.

9. Accuracy of Pre-set

A pre-set accuracy test is only conducted when it is necessary to check the accuracy of the pre-set delivery volume.

1. Condition the standard volume measure.
2. Enter and record a suitable pre-set value using the pre-set facility. This preset value should deliver close to the value of the reference standard measure being used.
3. Make a delivery at maximum achievable flow rate until the delivery stops. Record the volume indicated by the fuel dispenser (VFD) and the volume indicated by the working standard measure (VREF).
4. Calculate and record the relative error (EFD).
EFD = (VFD - VREF) / VREF X 100
5. Determine if the result is within the MPE.

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