Understanding the Effects of Salt Water on Pressure Testing for Plastic Pieces

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In summary, the question is whether the pressure felt by plastic pieces in a container of salt water will be affected by the salt water itself or if it changes when the container is sealed with air above the water. The answer is that the pressure at the bottom of a container filled with salt water is 14.7psi, and adding compressed air will increase the pressure by the amount of air pressure plus 14.7psi. For example, if 20psi of air is pumped in, the total pressure at the bottom would be 34.7psi. The water itself exerts a pressure based on its height, but the air pressure can be added on top. The container does not need to expand as air is compressible.
  • #1
TrueQ06
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I am trying to subject some plastic pieces to temperature and pressure testing while the parts are in a container of salt water. I have a pressure chamber that is pumped to a desired pressure with compressed air.

If I put the pieces in the container of salt water in the chamber and then pump it to 20psi, will the pressure felt by the parts be 20psi, or does the salt water affect the pressure the parts feel? Does that change if I seal the container with some air above the salt water?

Thanks.
 
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  • #2
If you had a container filled with salt water 33' high the pressure at the bottom would be 14.7psi. If the container was open to the air, the pressure at the bottom would be 29.4 psi. Pumping in compressed air would result in a rise in pressure equal to the pressure of the air plus the 14.7 psi of the water.

If you pumped in 20psi of air, as you suggest, then the pressure at the bottom would be 34.7psi. Thats assuming a 33' water column. You can do the math to adjust the pressure the water adds if the column is less than 33'. For example, a water column half as high (16.5') would be (7.35psi).
 
  • #3
If I get what you are saying, its like a ball of water in a box of air which you can pressurize?? Since water is incompressable, I think the water pressure would equal that of the air pressure assuming the 'ball' was made of flexible material.
 
  • #4
The water exerts a pressure all by it's self, depending on the height of the water column. Any air pressuer you add on top of the water will add to the total pressure. As far as the container expanding, that is not necessary as the air is compressable.
 

FAQ: Understanding the Effects of Salt Water on Pressure Testing for Plastic Pieces

What is pressure and how is it measured?

Pressure is defined as the force exerted per unit area on a surface. It is typically measured in units of Pascals (Pa) or pounds per square inch (psi). The most common tool used to measure pressure is a pressure gauge, which uses a diaphragm or spring to convert pressure into a mechanical movement that can be read on a scale.

How does pressure affect different materials?

The effect of pressure on a material depends on its properties, such as elasticity and compressibility. In general, increased pressure can cause materials to compress or deform, while decreasing pressure can cause materials to expand. Some materials, such as gases, are highly affected by pressure and can change state (e.g. from gas to liquid) under high pressure.

What are some real-world applications of pressure?

Pressure has numerous applications in everyday life and in various industries. Some examples include using pressure to inflate tires, pressurizing containers for food preservation, and using water pressure to power hydroelectric generators. In the medical field, blood pressure is an important indicator of overall health.

How is pressure related to fluid dynamics?

Fluid dynamics is the study of how fluids (liquids and gases) behave under different conditions, including pressure. Pressure is an important factor in determining the flow of fluids, as it can cause fluids to move from areas of high pressure to low pressure. This is known as fluid flow, and it plays a crucial role in the design and operation of many systems, such as pumps and pipelines.

What are the effects of pressure on the human body?

The human body is able to withstand a wide range of pressures, but extreme changes in pressure can cause discomfort or even harm. For example, high atmospheric pressure (such as in deep-sea diving or high-altitude flights) can cause ear pain and other physiological effects. In contrast, low pressure (such as in outer space) can cause the body to swell and can lead to serious health issues without proper protection.

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