Motor to Push Air into a Piston

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Discussion Overview

The discussion revolves around the design of a motor and pump system intended to maintain a constant air flow into a piston that is used to lift varying loads. The participants explore the challenges posed by the compressibility of air and the need for consistent performance despite changing pressures and loads.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant seeks a motor capable of pumping air into a piston at a constant speed while lifting loads between 10-200 lbs, expressing concern about how varying weights affect air pressure and pump speed.
  • Another participant questions whether the original poster is looking for a motor to power an existing pump or if they need a complete pump system, noting that a positive displacement air pump may not be feasible due to air's compressibility.
  • A third participant asks for additional details such as the required pressure, piston sealing, and specific rates of travel, suggesting that a motor/pump system with a pressure holding tank and control mechanism could be effective.
  • One participant agrees on the necessity of a feedback loop and mentions the potential benefit of an accumulator, while seeking clarification on whether the goal is to maintain a constant volume of air or a constant speed of the piston, highlighting the complexities introduced by air compression.

Areas of Agreement / Disagreement

Participants generally agree on the need for a feedback control mechanism and the challenges posed by air compressibility. However, there is no consensus on the specifics of the system design or the definitions of constant volume versus constant speed.

Contextual Notes

Participants have not established specific parameters such as required pressure or piston travel rates, which may affect the design considerations. The discussion reflects uncertainty regarding the feasibility of maintaining constant air flow under varying load conditions.

Who May Find This Useful

Individuals interested in pneumatic systems, motor design, or those facing similar challenges in maintaining consistent performance in variable load applications may find this discussion relevant.

omalleyt
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Alright. I need a motor that is capable of pumping air into a piston filled with compressed air. The motor needs to pump the air into the piston at a constant speed, as the piston is being used to raise up a load. The problem is that the weight of the load on the piston will be between 10-200 lbs. Since the weight of the load will change the pressure of the air in the piston, I'm concerned that it will also affect the speed at which the motor is able to pump in the air. I've already calculated that the motor needs to be at least 1/2 horsepower. Is there a way I can make sure the speed of the air pumped into the piston is constant?
 
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The way that is worded is a little confusing. Have you already constructed the pump and are looking for a motor to power it or are you looking for a pump?

In any case, since air is compressible, it isn't possible to construct a positive displacement air pump (a pump where the volume moved is always constant). The closest thing you can hope for is a variable speed pump with some sort of feedback control.
 
what pressure do you estimate that it would need? What travel thru the bore? How is the piston sealed? Does the piston need to go at a specific rate? How many times does the unit need to go up and down? Does the downward travel also need a specific rate of travel? As previously stated, a constant output pump will not work, it would need a constant pressure, and flow rate, and both would vary with the mass applied on top. My first impression would be to use a motor/pump, pressure holding tank, and a control mechanism to supply a set pressure, and displace the volumn as the piston raises.

dr
 
I agree that some sort of feedback loop is essential, and an accumulator would be of great help. One thing eludes me. Do you mean that the volume of delivered air must be constant, or the speed of the piston? Wouldn't those diverge during travel due to the compression factor?
 

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