Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. If you continue browsing the site, you agree to the use of cookies on this website. See our User Agreement and Privacy Policy.

Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. If you continue browsing the site, you agree to the use of cookies on this website. See our Privacy Policy and User Agreement for details.

Like this presentation? Why not share!

- Mig mag tech by Nguyen Tung 418 views
- Master slide for wis5 by Nguyen Tung 450 views
- Mac thep kiem tra pha huy by Nguyen Tung 537 views
- Mag tig welding (messer) by Nguyen Tung 680 views
- Phần iii phương thức quản lý thi cô... by Nguyen Tung 2424 views
- Phần iv những bài học kinh nghiệm by Nguyen Tung 1435 views

420 views

Published on

No Downloads

Total views

420

On SlideShare

0

From Embeds

0

Number of Embeds

1

Shares

0

Downloads

16

Comments

0

Likes

2

No embeds

No notes for slide

- 1. EVOLUTION OF REDUCING VALVES<br />DR.P.N.REDDY<br />2/24/2009<br />1<br />
- 2. INTRODUCTION<br />Anesthetic gases are compressed.<br />Must be reduced to working pressure.<br />Problems with high pressure:<br />Periodic adjustment of bobbin.<br />Fine adjustment difficult.<br />Delicate parts can be damaged.<br />Can damage the pt- barotrauma.<br />2/24/2009<br />2<br />
- 3. SIMPLE VALVE<br />2/24/2009<br />3<br />
- 4. SIMPLE VALVE<br />FORCE = PRESSURE × AREA<br />Force acting on area “ a “ due to pressure in the cylinder = Pa.<br />The upward forces acting on j rod is RA.<br />R=reduced pressure acting on diaphragm Y of area A of low pressure chamber L.<br />The outlet T on the side.<br />2/24/2009<br />4<br />
- 5. SIMPLE VALVE contd…,<br />If Pa > RA gas flow from HL<br />Pr in L raises Y & pr in L chamber; RA = Pa<br />Then gas stops flowing.<br />Pa =RA<br />R=Pa /A<br />R/P =a/A<br />2/24/2009<br />5<br />
- 6. SIMPLE VALVE contd…<br />When T is opened gas flows out reducing pr in chamber L & Pa increases & gas flows to chamber L<br />During administration of gases to pt pressure in chamber H decreases progressively.<br />if pr in H chamber reduced to p-p¹ & reduced pr R falls to R¹<br />2/24/2009<br />6<br />
- 7. P¹a = R¹A<br />R¹ = P¹ a/A<br />R¹P¹ = a/A<br />This shows ratio of decreased pressure to high pr is proportional to the ratio of area of high pr seating to area of low pr seating.<br />But a/A is fixed<br />Hence in simple valve as pr P falls the R reduced pr also falls proportionately. <br />2/24/2009<br />7<br />
- 8. So , the bobbin falls slowly with reduced flow rate.<br />This simple valve satisfies two points:<br />1. pressure is reduced<br />2. fine adjustment possible<br />But the bobbin needs frequent readjustments.<br />2/24/2009<br />8<br />
- 9. RATE OF FALL OF REDUCED PRESSURE<br />The fall of reduced pr is proportional to cylinder pr.<br />With full cylinder if 3 lt of flow is kept after completion of half cylinder the output is only 1.5 lt /min.<br />2/24/2009<br />9<br />
- 10. IMPROVED VALVE SCHEME 1<br />2/24/2009<br />10<br />
- 11. IMPROVED VALVE SCHEME 1<br />Z is high tension spring exerting downward pr S on diaphragm Y.<br />The force S can be changed by the screw Q.<br />Upward pr is RA.<br />Downward force is (Pa+S).<br />At equilibrium., RA = Pa + S = R(Pa+S) / A.<br />R=Pa/A + S/A .<br />2/24/2009<br />11<br />
- 12. Contd,…<br />The reduced pressure R now depends on downward force S.<br />S/A is the main factor controlling the reduced pr.<br />R can be adjusted to any level by varying the tension of the spring.<br />The rate of decrease of reduced pr depends on 3 factors :<br /> 1). P-P¹ <br /> 2). R <br /> 3). a/A<br />2/24/2009<br />12<br />
- 13. Contd…,<br />No control on P-P¹<br />Ratio of a/A can be controlled<br />R can be controlled by spring Z<br />The reduced pr R also depends on ratio of a/A<br />If a/A is reduced the rate of fall of R also decreases.<br />It is also observed that if R is set initially at high level the valve works better.<br />2/24/2009<br />13<br />
- 14. Contd,…<br />Therefore if the tension S is made very large compared to Pa the valve works better and rate of reduction of reduced pr R further decreases.<br />2/24/2009<br />14<br />
- 15. IMPROVED VALVE SCHEME 2<br />2/24/2009<br />15<br />
- 16. IMPROVED VALVE SCHEME 2<br />In the scheme 1 tap T is closed or partially opened to deliver small flows & so R falls slowly.<br />If large gas flows out of chamber L the R decreases faster. Such high flows are needed to run the ventilator,<br />A small spring s is placed below J rod and it can be adjusted to vary its tension with the help of thumb screw.<br />2/24/2009<br />16<br />
- 17. IMPROVED VALVE SCHEME 2<br />If cylinder is 132 atm pr the spring s fully closes the seating a and no gas flows to chamber L.<br />If z spring is unscrewed & T is opened the small spring s prevents air leak & pr in L is 0.<br />If z spring is screwed down it pushes small s down and gas flows into chamber L.<br />Here the nozzle size and seating area a is increased to give high flows.<br />But if the ratio of a/A decreases the valve cannot function efficiently.<br />Hence a is increased to a small extent & A is increased to large extent so that the ratio is maintained.<br />2/24/2009<br />17<br />
- 18. IMPROVED VALVE SCHEME 3<br />2/24/2009<br />18<br />
- 19. IMPROVED VALVE SCHEME 3<br />Here soft rubber metal diaphragm is replaced by a rigid hard diaphragm so that it can withstand greater changes in pressure.<br />The J rod is broken into two parts , the seating a and vertical rod x with a screw d .<br />The seating is adjusted & fixed at a level where there is no flow when z is not exerting any pr.<br />Here no small spring & R is zero.<br />2/24/2009<br />19<br />
- 20. IMPROVED VALVE SCHEME 3<br />The action of small spring s is taken over by diaphragm y.<br />When z spring is screwed down it produces tension S on the diaphragm and J rod and seating come down & gas flows into L.<br />Here downward forces are (Pa+S) & upward forces are RA<br />R= (Pa +S) /A<br />Advantages:<br />Metal diaphragm<br />R can be set at high level (4 kg/sq cm²)<br />2/24/2009<br />20<br />
- 21. IMPROVED VALVE SCHEME 4<br />2/24/2009<br />21<br />
- 22. IMPROVED VALVE SCHEME 4<br />2/24/2009<br />22<br />
- 23. IMPROVED VALVE SCHEME 4<br />IN 1890, CLARKSON designed a valve with a seating a in high pr side of the valve.<br />All levers rubber parts are eliminated.<br />Servicing became very easy.<br />The features are:<br />Seating a in high pr chamber<br />Presence of safety blow valve<br />High pr guage<br />Low pr guage<br />Diaphragm made of tough rubber.<br />2/24/2009<br />23<br />
- 24. IMPROVED VALVE SCHEME 4<br />The spring s is controlled by adjustable thumb screw.<br />This arrangement is suitable when R is kept high and it can be varied by the operator.<br />Here as the cylinder pr comes down the R slightly goes up and bobbin raises slightly higher and comes down to 0 as cylinder becomes empty.<br />2/24/2009<br />24<br />
- 25. IMPROVED VALVE SCHEME 4<br />2/24/2009<br />25<br />
- 26. Advantages of modern valves <br />To run ventilators.<br />To use with high resistant devices like vaporizers.<br />Bobbin will not fall n rise with IPPV<br />Periodic adjustment of bobbin not necessary<br />Slave valve mechanism with N2O <br />Pressure settings in manifold<br />2/24/2009<br />26<br />
- 27. Fire hazards<br />2/24/2009<br />27<br />
- 28. Thank u<br />Sorry for the boring lecture!!!<br />28<br />2/24/2009<br />

No public clipboards found for this slide

×
### Save the most important slides with Clipping

Clipping is a handy way to collect and organize the most important slides from a presentation. You can keep your great finds in clipboards organized around topics.

Be the first to comment