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Click On ASCO

52- Although, the plant voltage is constant, the air pressure does change throughout the day. Lets look at how changes in air pressure, affect the forces in an unbalanced valve. Click On ASCO.

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Click On ASCO

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  1. 52- Although, the plant voltage is constant, the air pressure does change throughout the day. Lets look at how changes in air pressure, affect the forces in an unbalanced valve. Click On ASCO

  2. 53- The Asco design is used by a number of valve manufacturers. Let’s look at how the valve operates. “Inlet Air” “Orifice” “PxA” VS “Spring”

  3. 54- The solenoid spring holds the poppet on seat and blocks the inlet air. Then depressing the exhaust spring, holding the exhaust poppet open.

  4. 55- The valve shifts depressing the solenoid spring allowing air to flow from the inlet to the outlet. At the same time closing the exhaust poppet.

  5. 56- With a long stroke solenoid our shifting forces are low. The force curve shows this relationship. “STATE”

  6. 57- With Mac’s short stroke solenoid, our shifting forces are HIGH. Like holding two magnets close together. “STATE”

  7. 58- Solenoid & spring forces are related. With a long stroke solenoid our shifting forces are low.

  8. 59 – “CLICK”

  9. 60- Therefore we must use a weak spring. This force relationship is shown with the bar graph & force curve.

  10. 61- With a short stroke solenoid our shifting forces are high. Therefore we can use a strong “beefy” spring.

  11. 62- Lets use the Mac test, to check the force of the Asco return spring.

  12. 63- The Asco spring force in voltage, is 1.4volts on a 24volt valve. This is 50% less then Mac’s minimum guidelines. Remember Mac uses 3v @ 24v 50v @ 120v

  13. 64- We’ve seen that a long stroke=low shifting forces. Lets see how changes in plant air pressure and contamination, affect the unbalanced Asco design.

  14. 65- With a fixed orifice, changes in air pressure will affect the shifting forces of the valve.

  15. 66- As the pressure increases the forces against the spring increase.

  16. 67- We see the force graph rise, as we increase the pressure to 40psi.

  17. 68- At 60psi, the pressure force is almost equal to the spring force.

  18. 69- At 90psi, the pressure force overcomes the spring and off-seats the valve. With this unbalanced design the forces to shift the valve change as the air pressure changes.

  19. 70- Lets show our valve force tester, with the Asco valve. Here we show 7ms response time at 24 volts.

  20. 71- At 13 volts our response time is 13ms.

  21. 72- At 36 volts our response time is 5ms. We can see how the response times have changed as we change the valve forces.

  22. 73- Now lets look at the valve forces, as we change the operating pressure of the Asco valve. At 20psi the valve shifts in 10ms.

  23. 74- At 60psi the forces have increased and the Asoc valve shifts in 8ms.

  24. 75- Now lets test the Mac BALANCED design at different pressures. At 20psi the valve shifts in 4ms.

  25. 76- At 60psi the Mac BALANCED design still shifts in 4ms.

  26. 77- Now we can see the differences in shifting forces between the Mac BALANCED design and the Asco un-balanced design. 1 2 3 4

  27. 78- The Mac balanced design was accomplished by making the area the same at the valve inlet.

  28. 79- Here we can see the forces (pressure x area) @ 20psi working against the same area in both directions.

  29. 80- @ 40psi, “CLICK”

  30. 81- @60psi, “CLICK”

  31. 82- @75psi, “CLICK”

  32. 83- 150psi the forces are still equal and opposite, cancel out each other and have no affect on the valve shifting forces.

  33. 84- We’ve seen how changes in air pressure affect shifting forces. Now lets see how valves are affected by air line contamination.

  34. 85- Let’s look at how unbalanced designs are susceptible to contamination.

  35. 86- “CLICK”

  36. 87- As the valve shifts, the exhaust path goes through the center of the solenoid.

  37. 88- Contamination is allowed to build up until the valve malfunctions. With A/C’s in-rush current, contamination will burn-out the solenoid.

  38. 89- Let’s look at contamination with Mac’s balanced design. “D” seals provide balance, protect the solenoid and perform a wiping action.

  39. 90- Let’s take a detailed look at how the Mac “D” seal performs these functions.

  40. 91- The wiping action is similar to a windshield wiper, not letting contamination build in the valve bore.

  41. 92- Mac’s “D” seal provides minimal friction by allowing closer manufacturing tolerances.

  42. 93- The “D” seals O.D. has 10 x better tolerances than typical “O” rings.

  43. 94- Mismatch & flash are not part of the sealing surface of the Mac “D” seal.

  44. 95- Mac case hardens their seals, to control the resistance to shifting. This resistance consists of, the rubber hardness, compression & the coefficient of friction.

  45. 96- A hard compound produces high resistance to shifting & high compression friction.

  46. 97- A soft compound produces drag or a high coefficient of friction.

  47. 98- Case hardening allows for a hard O.D. to keep resistance and friction low. While maintaining a soft core for sealing compression, which protects & separates the solenoid.

  48. 99- Another benefit of case hardening is the elimination of “creep”.

  49. 100- With a soft O.D. the rubber can “creep” into the peaks & valleys of the bore.

  50. 101- “CLICK”

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