Centrifugal Pumps & Blowers: Why Prime Pumps not Blowers?

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In summary: Gases can escape freely from a container whereas liquids will stay put unless acted upon by a force (in this case, air pressure). This means that when you prime a pump with a liquid, the liquid is already in a state where it is close to providing the pressure reduction that the pump needs in order to function.
  • #1
anshul144
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centrifugal pumps and blowers work on the same principal then why centrifugal pumps are needed to be primed but blowers are not?
 
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  • #2
Well I assume your view is a pump deals with liquid and blower with gas.

If there is no liquid in the pump (on the vanes) then it can't pump anything - it would just spin and do nothing. So you need to prime the pump by getting the fluid into it, so that once it is switched on it has something to pump.
 
  • #3
A blower is always primed!
 
  • #4
russ_watters said:
A blower is always primed!

Care to expand on that? What is the difference aside from one is primed and one isn't? What causes one to be always primed?
 
  • #5
Hi JaredJames.
JaredJames said:
Care to expand on that? What is the difference aside from one is primed and one isn't? What causes one to be always primed?
I think it's exactly as you already pointed out:
JaredJames said:
Well I assume your view is a pump deals with liquid and blower with gas.
Generally when people talk about pumps, they're talking about a machine that moves liquid. Similarly, when referring to blowers, they're talking about machines that move gas. Also, we would naturally assume the blower to have air in it before it starts up, hence it is already "primed", whereas a pump that has air in it is starting out with the wrong working fluid.

I think more fundamentally, the reason a centrifugal pump can't generally self prime is because of the way it creates pressure - by accelerating a given fluid. If the fluid is a liquid, it is almost certainly going to be much more dense than a gas and hence it will produce much more pressure accelerating a liquid. If a centrifugal liquid pump is spinning with air in it, the amount of pressure it creates is very small, so most systems they are placed in won't flow until there's enough pressure to get the fluid to move.
 
  • #6
Cheers.
 
  • #7
AS far as I can see it, the reason that you may need to prime a (liquid) pump is that there would not be enough pressure reduction in the expanding volume inside the pump to produce sufficient lift if it were just full of air. If it is full of liquid then the pressure reduction could be much more as the volume is increased - allowing the lifting process to start.
This argument also applies in a centrifugal pump in which air is not dense enough to produce a sufficient pressure difference as it is thrown out by the spinning vane.
 
  • #8
JaredJames said:
Care to expand on that? What is the difference aside from one is primed and one isn't? What causes one to be always primed?
You need to prime a pump becuase it isn't full of liquid and isn't capable of generating enough vacuum to pull the liquid into itself. A blower/fan is always full of air unless it is in space.
 
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  • #9
It's all to do with the cohesion in liquids compared with no cohesion in gases.
 

1. What is the difference between centrifugal pumps and blowers?

The main difference between centrifugal pumps and blowers is the direction of gas or liquid flow. In centrifugal pumps, the flow is radial, meaning it moves away from the center of rotation. In blowers, the flow is axial, meaning it moves parallel to the axis of rotation.

2. Why are centrifugal pumps preferred over blowers for priming pumps?

Centrifugal pumps are preferred for priming pumps because they can create a lower pressure at the inlet, allowing them to draw in air and prime the pump quickly. Blowers, on the other hand, are designed for higher pressure applications and may not be able to generate enough suction to prime the pump effectively.

3. Can blowers be used to prime pumps in certain situations?

Yes, in some cases, blowers can be used to prime pumps. However, this is typically only done when the pump is located above the liquid level and there is no other option for priming. In this scenario, the blower creates a vacuum to draw the liquid up into the pump and prime it.

4. Are there any advantages to using blowers instead of centrifugal pumps for priming?

One potential advantage of using blowers for priming is that they can handle larger volumes of gas or liquid. This can be beneficial in certain applications where a large amount of priming is required. Additionally, blowers may be more energy-efficient in some cases.

5. What are some common applications for centrifugal pumps versus blowers?

Centrifugal pumps are commonly used for moving liquids, such as water, chemicals, and oil, in industrial, commercial, and residential settings. Blowers, on the other hand, are often used for aeration, ventilation, and pneumatic conveying in industries such as wastewater treatment, mining, and manufacturing.

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