3 replies to this topic

hi friends!!


we see on petrol stations,an electronic meter which shows volume of petrol/diesel being fed into our automobiles' fuel tank....
but wat basically the meter is dat is calibrated with the electronic meter..??
is it rotameter,venturi meter,orifice meter...or ny other meter...???

[JMW]

hi friends!!


we see on petrol stations,an electronic meter which shows volume of petrol/diesel being fed into our automobiles' fuel tank....
but wat basically the meter is dat is calibrated with the electronic meter..??
is it rotameter,venturi meter,orifice meter...or ny other meter...???

Positive displacement meters are very accurate over wide range of flow rates.
Many custody transfer flow meters or weights and measures approved meters, such as are used for tank truck delivery of heating oil or LPG are often single element positive displacement meters, piston or gear types but for petrol even greater precision is achieved using multiple pistons all connected to a crank which controls an arrangement of valves (often a sliding valve plate).
Each cylinder has fluid throughout its capacity and the piston, as it moves up and down the chamber, fluid is displaced from the chamber ahead of it to the discharge and fluid enters the cylinder behind it from the inlet. As the piston reaches the top or bottom of its stroke, the valves change over such that the inlet and outlet porting is reversed.
A feature of positive displacement meters is that some fluid can flow through the working tolerances but in this type of meter the piston may be fitted with an elastomer seal to limit or eliminate such flow.
Perhaps the most accurate of these meters is that manufactured by Avery Hardol, now part of the Alan Cobham Flight refuelling group and formerly part of GEC and which are used for aviation fuels.
Manufacturers other wise include Schlumberger and Tokheim but used to include Brodie and many others.

Positive displacement meters are volumetric, that is, they measure the volume flow of fluid. It is suggested that filling your car in cold weather will gain for you more fuel than in warm weather but consider that petrol is usually stored in underground tanks where the temperature variations are not major. Tank truck meters may, however, include temperature compensation and in some applications are being replaced by coriolis mass flow meters. In others, density measurement is sometimes used to compensate the volumetric measurement.

If you search the internet for "positive displacement meters" you will find several sites that include an animation which will demonstrate the basic principle. It may be a little harder to find one that illustrates a multiple piston meter though, there seems to be some confusion in many web sites between nutating an oscillating piston meters and reciprocating meters. I did a quick search and didn't find any examples in the first pages of an advanced search.
I'd suggest noting the manufacturers name on your local petrol pump, finding them and requesting more detailed information from them.

[JMW]

Try this website for a sectioned view:
http://www.tcsmeters...Manual.Rev5.pdf
Note that the valve action is here controlled by what they call a "wobble plate".
Note also thet the pistons are little more than discs since they have very little pressure drop to contend with.

[JMW]

One article suggests that the reciprocating piston meter is one of the earliest forms of positive displacement meter, and (if one ignores the Shaduf), this is possibly true.
The reciprocating meter design probably owes a lot to the inspiration of the steam engine piston and valve gear and when first produced the visual similarities are strong. I'm thinking here of a picture of a water meter supplied by Tylors of London to the Shanghai water company in the 1860s. This is the company that later introduced the Patent British Water Meter, a rotary piston design which is the basis for many water meters today and many industrial meters also.

But that's probably more than you wanted to know.....