1. Pascal’s Law & 5/2-way impulse valve, pneumatically operated
Lesson 7

2. After successfully completing Lesson 7, you will be able to:
Explain the theory of Pascal's law.
Use Pascal's law to calculate pressure, force, and area.
Explain the force triangle.
Explain how a pneumatically actuated 5/2-way impulse valve operates.
Build and operate a circuit diagram that requires a 5/2-way impulse valve, pneumatically operated.
Apply connection lines and simulate a pneumatic circuit.

3. Pascals Law I
Around 1650 a French scientist named Blaise Pascal discovered a basic physical law dealing with fluids. Pascal’s law stated that, “A pressure added to a confined fluid is transmitted undiminished throughout the fluid. The pressure acts on all surfaces in a direction at right angles to those surfaces.” This law explains that air, when contained and pressurized, reacts equally against all the surfaces of a container no matter what shape of the container. Pascal’s law provides us with a formula that can be used to determine the force exerted by an actuator at a certain psi. The formula can also provide information about the pressures and the piston size of an actuator that might be needed to perform a specific amount of work.

4. The formula is usually written with letters that represent the three specific factors described in the law; Pressure, Force and Area. The units of measurement are important factors when using Pascal’s Law. Pressure should be in psi, force should be in pounds and area should be represented in square inches (in2).
PRESSURE = FORCE/AREA (P=F/A)
Using algebraic manipulation, the formula can be configured to find Pressure, Area or Force, as long as two of the factors are known.

5. Force Triangle
It is easy to get confused when figuring a cylinder problem, so try to use the Force triangle to help you determine which formula to use for a specific problem. The Force triangle is a partitioned line drawing used to indicate any one of the three algebraic expressions of Pascal’s Law.

6. To use the Force triangle, put your finger over the letter you wish to find, and follow the indicated calculation with the remaining letters. For instance, covering the letter F, leaves P x A to find the answer to a force problem. Covering the letter A to solve for an area leaves F/P. Use your calculator and Pascal’s Law to calculate the missing theoretical pressure illustrated by the following graphic of the problem: What would the theoretical pressure requirement be to create 250 lbs. of force using a cylinder with a piston area of 2 in²?

7. To begin solving this problem, you must first identify the unknown factor. Psi is the unknown; so formulate your problem by following the calculation strategy;
Cover the P on the Force triangle to find the correct formula
Substitute in the known factors (force and area)
Calculate the answer

8. Fundamental Pneumatic Principles
The Force triangle indicates that the formula needed is: P = F/A Known factors substitute as P = 250 lb./2in² The answer shows that the theoretically, a system pressure of 125 psi will press against a 2 in² piston area with a force of 250 lbs. Solve for Area: What would be the theoretical piston area requirement to create 500 lbs. of force using 100 psi of cylinder pressure? Looking at the triangle, we see that A = F/P A = 500lbs/100psi A = 5 in² The answer shows that theoretically, a system pressure of 100 psi will press against a 5 in² piston area with a force of 500 lbs.

9. Solving for Force
What would the theoretical exerted force be from a cylinder that has a 5 in² piston with a system pressure of 60 psi.
F = P x A
F = 60 psi x 5 in²
F = 300 lbs. of Force
Lesson:
In the lesson, you will use the FluidSIM program to create and simulate a working pneumatic circuit using a 5/2-way impulse valve, pneumatically operated. The valve is controlled by receiving a signal through both piloted ports—port 12, which allows airflow from ports 1 to 2; and port 14, which allows airflow from ports 1 to 4. The valve remains operative until an opposing signal is received