You'll need to be more specific, since valves are used in many different applications.
What type valves are you posting your inquiry?
Since the topic is under "new electrical work", one might assume that you are asking about electrically operated valves or valves with position sensors, or you may be asking about the old "vacuum tubes", which in much of the world are referred to as "valves".
Answering all of those questions would end up being a dissertation, and probably more than would be appropriate for Answers.com
The valves of the heart prevent the blood that is pumped out from flowing back to the heart or backward in veins.
using valves
using valves
using valves
They would be considered incompetent valves because they are not working properly. You need all the vein valves to work properly for maximum functioning.
Valves - allow fluids or gases to only flow in one direction. They're control devices.
exhoust vave
It will go in the valves but it's not good for your Trumpet..
veins have valves because they bring blood from the bottom half of your body and valves stop the back flow of blood since the veins work against gravity.
Bicycle tube valves are one-way valves. They let air pass one way, then holds it in.
The way the valves on a brass instrument work is that when pressed down they allow air to pass through a piece of tubing, thus making the length of tubing of the trumpet longer, this allows valved instruments to be able to play more notes than instruments without valves.
The link below will answer all questions.
Yes, they do. They are exactly the same. The pig heart valves will last about 15 years. Sometime cows are used for these xenotransplants.