What is the force on a poppet valve due to expanding air?

In summary, the conversation discusses a problem with a poppet valve that is initially closed over a vent and then pushed open by a force applied to the valve by a pushing rod. The air inside the container at P1 is expanding through the valve to atmospheric pressure. There is also a spring on the rod resisting this expansion. The main issue is determining the force on the poppet valve due to the expanding air, and how this force changes as the pressure and mass flow through the valve decreases. It is suggested that the pressure on the poppet can be altered by adjusting the geometry of the valve or using a relief valve with a huddling chamber.
  • #1
tommy101
2
0
I need help with the following problem. I have attached a rough sketch showing what I'm looking at. Basically a popppet valve is closed over a vent. It is then pushed open by a force applied to the valve by the pushing rod. Their is a spring on the rod resisting this and providing a force labeled Fspring. The air inside the container at P1 is then expanding from rest through the valve to Pa (atmospheric). What i am trying to work out, and can't find a formula anywhere for, is what the force on the poppet valve will be due to the expanding air (Ffluid). I'm trying to model this system and currently the valve won't stay open as i can't compute the force on the poppet valve accuratley.
 

Attachments

  • poppet.bmp
    76.6 KB · Views: 681
Engineering news on Phys.org
  • #2
The spring force, equal and opposite.
 
  • #3
Cyrus said:
The spring force, equal and opposite.

Yes it will be when the valve initially opens. But the pressure in the bag (P1) then decreases, the mass flow through the poppet will decrease, so the force on the poppet will decrease. Thats what I'm trying to work out. I need to know the force on the poppet to work out when the valve closes again.
 
  • #4
The valve will close when the pressure force is less than the force needed to deflect the spring.
 
  • #5
In designs like you show, the velocity of the fluid increases as it aproaches the curtain area, so the pressure across the face of the poppet drops (think Bernoulli's principal) even though you may not measure a decrease in pressure directly upstream of the poppet. The result is the force on the poppet will decrease with increased flow.

Things can be done to change this. Relief valves for example, have a 'huddling chamber' downstream of the curtain area which effectively increases the area, resulting in a higher force on the poppet from the fluid which pops the valve open (even though the spring load also increases per k*dx). Similarly, adjusting poppet and valve geometry can provide different pressure forces on the poppet as the valve opens. Careful control of the geometry can change the pressure load as a function of lift.
 

Related to What is the force on a poppet valve due to expanding air?

1. What is a poppet valve?

A poppet valve is a type of valve used in engines to control the flow of air or fuel. It consists of a disc-shaped valve head that sits on top of a valve seat and opens and closes to allow or prevent the flow of gases.

2. What are the forces acting on a poppet valve?

The main forces acting on a poppet valve are the opening and closing forces, which are caused by the pressure difference between the intake and exhaust sides of the valve. There are also forces due to the motion of the valve, such as inertia and friction.

3. How does the shape of the poppet valve affect the forces acting on it?

The shape of the poppet valve can affect the forces acting on it in several ways. A larger valve head can create more resistance to airflow, resulting in higher forces. The angle of the valve head can also affect the balance of forces, with a steeper angle creating more opening force and a shallower angle creating more closing force.

4. What factors can cause excessive forces on a poppet valve?

Excessive forces on a poppet valve can be caused by various factors, including a faulty valve spring, incorrect valve timing, or an incorrect valve size. These can result in the valve being unable to open or close properly, leading to increased forces and potential damage to the valve or engine.

5. How can the forces on a poppet valve be controlled?

The forces on a poppet valve can be controlled by adjusting the valve timing, using the correct size and shape of valve, and ensuring that all components, such as the valve spring, are in good working condition. It is also important to regularly maintain and clean the valve to prevent buildup of debris that could affect its operation and force balance.

Similar threads

Low Viscosity Oil, Tanks, Pressure Relief Valves and Check Valves
    • Mechanical Engineering
Replies
2
Views
362
Force from Water Entering a Pressurized Tank with No Relief Valve
    • Mechanical Engineering
Replies
8
Views
1K
Just curious about many things like hydrostatics
    • Mechanical Engineering
Replies
28
Views
2K
Centrifugal Pump: Water Pressure at 50m & 4 Bar Gauge
    • Mechanical Engineering
Replies
4
Views
1K
Temperature after closing the valve
    • Engineering and Comp Sci Homework Help
Replies
8
Views
1K
Need Advice: Passing a Ball Bearing from Air to Water
    • Mechanical Engineering
Replies
3
Views
1K
Rotary Vane Vacuum Pump Question
    • Mechanical Engineering
Replies
5
Views
1K
What is the Best Control System for Compressed Air in a Drone?
    • Mechanical Engineering
Replies
1
Views
2K
How much air is required to transfer liquid?
    • Mechanical Engineering
Replies
3
Views
1K
Sizing Needle Valves for Air Flow | 0.025 m^3/s
    • Mechanical Engineering
Replies
5
Views
8K

Hot Threads

Recent Insights

Back
Top