Positive displacement meters are in the category of flow quantity meters. They are used mostly when we desire excellent repeatability and high accuracy. Even they can used for high viscosity fluids with high accuracy and the pulsation in the flow rate will not affect the accuracy in any account. This types of flow meters comes under the category of the mechanical flow meters in which one or more moving parts are introduced in the flow path.
Principle of operation
When the liquid passes through the meter it will forces to moves a measuring element, this measuring element is consists of measuring chambers having a fixed volume. As because of this movement of measuring element moves, this compartments will fills and drains.thus For each movement or cycle, a limited amount of liquid is passed through the inlet to outlet of the instrument. By using a pointer number of cycles of measuring element is noted and is fed to a digital totaliser through an adjustable gearing set up. There are many meters using the principle of positive displacement meter, some of them are:-
When the liquid passes through the meter it will forces to moves a measuring element, this measuring element is consists of measuring chambers having a fixed volume. As because of this movement of measuring element moves, this compartments will fills and drains.thus For each movement or cycle, a limited amount of liquid is passed through the inlet to outlet of the instrument. By using a pointer number of cycles of measuring element is noted and is fed to a digital totaliser through an adjustable gearing set up. There are many meters using the principle of positive displacement meter, some of them are:-
1: Reciprocating piston type
2: Oval gear type
3: Nutating disc type
2: Oval gear type
3: Nutating disc type
Oval gear type flow meter
This also a quantity type meter which works on the principle of positive displacement meter. The materials used in this type meters are bronze, stainless steel, aluminium etc. size range 10mm to 40mm.
This also a quantity type meter which works on the principle of positive displacement meter. The materials used in this type meters are bronze, stainless steel, aluminium etc. size range 10mm to 40mm.
Construction
Two oval gear wheels are inter meshed and which rotates as a result of liquid flow through the meter. This rotation of wheel is fed to a counter by using a spindle. Only limited parts are in contact with liquid in this meter they are meter body, measuring chamber and oval gear wheels. These are usually made of anti corrosive metals or stainless steel or something like that.
Two oval gear wheels are inter meshed and which rotates as a result of liquid flow through the meter. This rotation of wheel is fed to a counter by using a spindle. Only limited parts are in contact with liquid in this meter they are meter body, measuring chamber and oval gear wheels. These are usually made of anti corrosive metals or stainless steel or something like that.
Nutating disc type
This type of meter also uses the principle of positive displacement meter. This meter is also known as disc meter. Used mainly for residential applications.
ConstructionThe disc used in the meter are usually made of moulded hard rubber.The disc drives in a circulatory zig-zag movement which entraps and allows liquid flow. From the name it self we can understand that in this type meter the disc is Nutating or wobbling. At operation time an amount of liquid is flows in and at the same time an amount liquid is going out. A digital totaliser or register is introduced to detect the disc movement which is transmitted to register by using the means of a transmitting gear.
Size of pipe is small amd maximum capacity is 1500gpm.
Advantages
* Cost is very low.
* Used in moderate pressure loss.
* Wide availability of materials for construction.
* Cost is very low.
* Used in moderate pressure loss.
* Wide availability of materials for construction.
Disadvantages
* Accuracy fair.
* Applicable only for clean water.
* pipe size and capacity is limited.
* Accuracy fair.
* Applicable only for clean water.
* pipe size and capacity is limited.
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