Simple Hydraulics & Pressure trouble

  • Context: Undergrad 
  • Thread starter Thread starter 3trQN
  • Start date Start date
  • Tags Tags
    Hydraulics Pressure
Click For Summary

Discussion Overview

The discussion revolves around a problem involving hydraulics and pressure related to a piston in a tube. Participants explore the challenges of calculating the pressure needed to lift a piston that does not have a complete seal, as it is smaller in diameter than the tube. The context includes considerations of atmospheric pressure and the implications of piston design.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant describes a scenario where a mass behaves like a piston in a tube, questioning the pressure required to lift it without a seal.
  • Another participant notes that piston rings are used to seal gaps in engines, implying that sealing is crucial for effective pressure application.
  • Further discussion highlights that even with piston rings, there can still be issues with pressure loss, referred to as blow back.
  • A participant shares a personal experience with a high-performance engine, mentioning specific measurements and the resulting inefficiencies due to ring gaps.

Areas of Agreement / Disagreement

Participants acknowledge the importance of sealing in piston design, but there is no consensus on how to address the specific problem of calculating pressure in the absence of a seal. The discussion reflects multiple perspectives on the implications of piston design and pressure loss.

Contextual Notes

The discussion does not resolve the mathematical steps needed to calculate the required pressure, nor does it clarify the assumptions regarding the fluid dynamics involved in the scenario presented.

3trQN
Messages
337
Reaction score
1
Im having a spot of trouble with some pretty elementary problem.

A mass sits inside a tube which is pointed vertically, the mass is the same shape as the pipe ( i.e. it behaves like a piston ), but the piston diameter is less than that of the pipe.

In order to lift the piston, what pressure must be applied to the fluid?

http://img235.imageshack.us/img235/4540/piston1lh2.th.jpg

The top of the chamber is eventually open to the atmosphere, and is filled with air at STP.

My problem seems to be the lack of a seal about the piston, i can see that it would be simple to calculate if it was simplified to a sealed piston, but with a piston that's smaller than the bore of the chamber its harder.
 
Last edited by a moderator:
Physics news on Phys.org
And that, essentially, is why engines have piston rings to seal that gap.
 
Yep, and even with piston rings you still get blow back.
 
Yeah. How irritating. That 650 hp 440 in my Roadrunner has a .008 ring gap (race-only TRW pistons), and it still wastes tons of potential through that.
 

Similar threads

Undergrad Steam flow rate in 2-chamber steam engine system
  • · Replies 4 ·
Replies
4
Views
2K
Graduate Pressure Increase with Diameter Decrease?
  • · Replies 2 ·
Replies
2
Views
6K
Hydraulics problem - calculate pressure at different points
  • · Replies 2 ·
Replies
2
Views
3K
Undergrad Pressurization rate vs. Mass Flow rate
  • · Replies 3 ·
Replies
3
Views
2K
How Do I Calculate Pressure Loss in Hydraulics with Two Pipes?
  • · Replies 22 ·
Replies
22
Views
4K
How Does a Hydraulic Lift Work with Different Piston Sizes?
  • · Replies 1 ·
Replies
1
Views
5K
HVAC Understanding the movement of a fluid in a vertical pipe
  • · Replies 10 ·
Replies
10
Views
6K
Quick Questions on Fluids: Pressure, Density, and Hydraulic Lifts Explained
  • · Replies 5 ·
Replies
5
Views
6K
Calculating Pressure for a Hydraulic Lift: A Scientific Approach
  • · Replies 12 ·
Replies
12
Views
3K
Explain the pressure terms in Bernoullis Equation
  • · Replies 18 ·
Replies
18
Views
10K