## Frequency of a spring = reed valve

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Rocket Man
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### Frequency of a spring = reed valve

MIT Professor Walter Lewi's Physics 801 Lecture10

You need to copy and paste the link to get the video to play. I tried all the options URL and Img nothing lets the video play just by clicking it.

Hooke's Law = frequency of a spring

F = Frequency

T = time in seconds

triangle symbol = delta

mg = gravity

M = mass

X = spring extention or movement

k = delta F/delta X = newtons per second

F = 1/T

F = mg when the spring is at rest

T = (2 x pi) times square root of (m/k)

dynajetjerry
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### Re: Frequency of a spring = reed valve

I just got into this thread and feel compelled to insert a few comments.
Based on our operations at Tenney's Aeromarine Co. in the late 1940s, the resonating frequencies of pulsejet reed valves should NOT be major factors in the designing of pjs, with a few limitations. For instance, the Argus in the V-1 ran at about 45-50 cps but their reeds resonated at about 215; the D-J/DFG reeds resonated at about 235 cps but the former ran at about 250 and the latter at about 115. Their reeds and retainers were identical! Further, we also fiddled with pjs that were 18 in. to 20 feet long, employing the above reeds and retainers. they ran at 300 to 20 cps! Of course, the useful lives of reeds in those pjs varied all over the map, being as much as 20 hours for the long engines and as little as 3 min. for the short ones.
Jerry Wiles
Louder is always better.

Rocket Man
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### Re: Frequency of a spring = reed valve

I have been doing research on valved pulse jet engines since 1970. You are correct most PJ engines will run no matter what the valve frequency is but the engines run best if the valves are closed when the engine fires. If the engine fires with the valves open the increased combustion chamber pressure slams the valves shut then you get valve damage and the valves are worthless in 2 or 3 minutes. A properly designed engine the valves will run for 20 hours and the valves still appear to be in almost brand new condition. Reed valve should open and close like the legs on a rocking chair. Test show all pulse jets have an unstable frequency with a suction fuel system, a tuned body frequency of 200 HZ will pulse in the range of 196 to 204. A fuel injection pressure regulated fuel system will pulse much closer to the target 200 Hz. The valve retainer limits how far the valves open and this will determines the operating frequency of the valves. The valve spring material, thickness, width, length all determine the valve frequency too but if the retainer stops the valve from opening past a certain point the retainer becomes the determining factory in the valve frequency. If the valves open too far they slam shut too hard causing valve damage. If the air intake holes under the valves are too large the valve bow like a dish when they slam shut on the holes. If the air intake holes are kept below a certain size determined by the frequency of the engine and metal thickness of the valves and engine can run for many hours with no damage to the valves.

Jobshopper
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### Re: Frequency of a spring = reed valve

First of all I'd like to thank everyone that have contributed to the pulse-jet forums, I've had good results all due to the questions comments and banter on this site. I do have a valve related question I'm at 8,200 feet elevation, where will my problems arise in putting a Argus type valve grid in a 20 to 50 pound range engine.
The few valvless I've built I really didn't alter the original design to accommodate for altitude. The time it took to fab them up was minimal and if I bombed out I was really out only a few hours of watching it snow.
Machining a valve head is a little more consuming and I'd appreciate hearing views and any numbers that members would like to hammer out ( for enjoyment) would be helpful..
Again I'd like to thank the core crew that have gone the extra mile to PROVE THEIR RIGHT. Reading through the pages of this forum has been at times more entertainment than usable info, all fun!!
Cory