ROOTS BLOWER- A POSITIVE DISPLACEMENT MACHINE
CENTRIFUGAL BLOWERS & FANS:
This Range covers various types of Centrifugal and Axial Flow Fans, which have relatively
high air displacement but low compression ratios. They are either of Centrifugal type, Axial
flow types or Regenerative types. As their internal clearances are relatively high, the discharge
pressures are limited to few inches of water only. These types are generally used for
applications requiring high volumes but low pressures such as in Air-conditioning, in
furnaces, Low pressure Cooling, Dust or Fume extraction systems, lean phase pneumatic
conveying etc
POSITIVE DISPLACEMENT BLOWERS (Roots Blowers):-
Twin Lobes and Three Lobes type Blowers
fall under this category. They have higher POSITIVE DISPLACEMENT BLOWERS (Roots Blowers):-
Twin Lobes and Three Lobes type Blowers fall under this category. They have higher efficiency at moderate compression ratios and are most efficient in the compression ratios of 1.1 to 2. They find use in applications, which require relatively constant flow rate at varying discharge pressures. These are generally available f o r c a p a c i t i e s 1 0m3 / h r – 10,000m3/hr for pressures up to 1Kg/cm2 (g) in single stage c ons t r uc t i on. They a r e e x t e n s i v e l y u s e d i n appl i c a t i ons such a Pneumatic Conveying, Aeration in ETP, Cement plants, Water Treatmentplants for filter backwash,
Aquaculture, aeration etc. efficiency at moderate compression ratios and are most efficient in the compression ratios of 1.1 to 2. They find use in applications, which require relatively
constant flow rate at varying discharge pressures. These are generally available f o r c a p a c i t i e s 1 0m3 / h r – 10,000m3/hr for pressures up to 1Kg/cm2 (g) in single stage c ons t r uc t i on. They a r e
e x t e n s i v e l y u s e d i n appl i c a t i ons such a s Pneumatic Conveying, Aeration in ETP, Cement plants, Water Treatment plants for filter backwash, Aquaculture, aeration etc.
COMPRESSORS:
BASIC TWIN LOBE ROTARY AIR BLOWER PRINCIPLE
Reciprocating, Vane or Screw Type Compressors are the machines in which compression
ratios are high – generally more than 2.5. These are generally required for applications
requiring low airflow but high pressures such as Pneumatic Tools, Solenoid Valves, Paint
shops, Drilling rigs etc.
This article is focused on Twin Lobe Blowers also popularly know as Roots Blowers-on the
name of its inventors. TWIN Lobe Rotary Air Blowers belong to the category of Positive
Displacement Blowers. They consist of a pair of involute profiled (shape of 8) lobes/rotors
rotating inside an oval shaped casing, closed at ends by side plates. One lobe is the driving lobe,
which is driven by the external power while the driven lobe is driven by a pair of equal ratio
gears. Both the lobes thus, rotate at same speed but in opposite direction.
As the rotors rotate, air is drawn into inlet side of the cylinder and forced out the outlet side
against the system pressure. With each revolution, four such volumes are displaced. The air,
which is forced out, is not allowed to come back due to the small internal clearance within the
internals of the machine except a very small amount called 'SLIP'. There is no change in the
volume of the air within the machine but it merely displaces the air from the suction end to
the discharge end, against the discharge system resistance i.e. no compression takes place in
the machine. Since the lobes run within the casing with finite clearances, no internal
lubrication is required. The air, thus, delivered is 100% Oil Free. These blowers deliver,
practically, a constant flow rate independent of the discharge pressure conditions. The flow
rate is dependent, largely on the operating speed.
Due to these constructional features it has the following distinct characteristics.
?The flow is largely dependent on the operating speed
?The input Power is largely dependent on the total pressure across the machine.
?The Suction & Discharge pressures are determined by the system conditions.
?The temperature rise of the discharge air & machine is largely dependent on the
differential pressures across it.
THERE is no compression or change in volume within the machine but the blower works
under system back pressure conditions. To illustrate further, let us consider a case when the
discharge of a blower is connected to the bottom of a tank, having water to a depth of 'H' mm.
The air-discharged accumulates in the discharge line until sufficient pressure is built (slightly
over 'H' mm of WG), when it starts to escape out. The system resistance or the static load on
the Blower is thus 'H' mm WG. The power consumed by the blower depends upon the flow
rate and the total pressure head on the Blower.
This Range covers various types of Centrifugal and Axial Flow Fans, which have relatively
high air displacement but low compression ratios. They are either of Centrifugal type, Axial
flow types or Regenerative types. As their internal clearances are relatively high, the discharge
pressures are limited to few inches of water only. These types are generally used for
applications requiring high volumes but low pressures such as in Air-conditioning, in
furnaces, Low pressure Cooling, Dust or Fume extraction systems, lean phase pneumatic
conveying etc
POSITIVE DISPLACEMENT BLOWERS (Roots Blowers):-
Twin Lobes and Three Lobes type Blowers
fall under this category. They have higher POSITIVE DISPLACEMENT BLOWERS (Roots Blowers):-
Twin Lobes and Three Lobes type Blowers fall under this category. They have higher efficiency at moderate compression ratios and are most efficient in the compression ratios of 1.1 to 2. They find use in applications, which require relatively constant flow rate at varying discharge pressures. These are generally available f o r c a p a c i t i e s 1 0m3 / h r – 10,000m3/hr for pressures up to 1Kg/cm2 (g) in single stage c ons t r uc t i on. They a r e e x t e n s i v e l y u s e d i n appl i c a t i ons such a Pneumatic Conveying, Aeration in ETP, Cement plants, Water Treatmentplants for filter backwash,
Aquaculture, aeration etc. efficiency at moderate compression ratios and are most efficient in the compression ratios of 1.1 to 2. They find use in applications, which require relatively
constant flow rate at varying discharge pressures. These are generally available f o r c a p a c i t i e s 1 0m3 / h r – 10,000m3/hr for pressures up to 1Kg/cm2 (g) in single stage c ons t r uc t i on. They a r e
e x t e n s i v e l y u s e d i n appl i c a t i ons such a s Pneumatic Conveying, Aeration in ETP, Cement plants, Water Treatment plants for filter backwash, Aquaculture, aeration etc.
COMPRESSORS:
BASIC TWIN LOBE ROTARY AIR BLOWER PRINCIPLE
Reciprocating, Vane or Screw Type Compressors are the machines in which compression
ratios are high – generally more than 2.5. These are generally required for applications
requiring low airflow but high pressures such as Pneumatic Tools, Solenoid Valves, Paint
shops, Drilling rigs etc.
This article is focused on Twin Lobe Blowers also popularly know as Roots Blowers-on the
name of its inventors. TWIN Lobe Rotary Air Blowers belong to the category of Positive
Displacement Blowers. They consist of a pair of involute profiled (shape of 8) lobes/rotors
rotating inside an oval shaped casing, closed at ends by side plates. One lobe is the driving lobe,
which is driven by the external power while the driven lobe is driven by a pair of equal ratio
gears. Both the lobes thus, rotate at same speed but in opposite direction.
As the rotors rotate, air is drawn into inlet side of the cylinder and forced out the outlet side
against the system pressure. With each revolution, four such volumes are displaced. The air,
which is forced out, is not allowed to come back due to the small internal clearance within the
internals of the machine except a very small amount called 'SLIP'. There is no change in the
volume of the air within the machine but it merely displaces the air from the suction end to
the discharge end, against the discharge system resistance i.e. no compression takes place in
the machine. Since the lobes run within the casing with finite clearances, no internal
lubrication is required. The air, thus, delivered is 100% Oil Free. These blowers deliver,
practically, a constant flow rate independent of the discharge pressure conditions. The flow
rate is dependent, largely on the operating speed.
Due to these constructional features it has the following distinct characteristics.
?The flow is largely dependent on the operating speed
?The input Power is largely dependent on the total pressure across the machine.
?The Suction & Discharge pressures are determined by the system conditions.
?The temperature rise of the discharge air & machine is largely dependent on the
differential pressures across it.
THERE is no compression or change in volume within the machine but the blower works
under system back pressure conditions. To illustrate further, let us consider a case when the
discharge of a blower is connected to the bottom of a tank, having water to a depth of 'H' mm.
The air-discharged accumulates in the discharge line until sufficient pressure is built (slightly
over 'H' mm of WG), when it starts to escape out. The system resistance or the static load on
the Blower is thus 'H' mm WG. The power consumed by the blower depends upon the flow
rate and the total pressure head on the Blower.
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