# Re: Beginner's lessons - Misguided Advice

```>The assertion: That a needle valve is not a valve unless the gas passing
>through it reaches the speed of sound.
>
>That is the assertion that I ridiculed. Prove me wrong.

"Well that would be real easy.  I can start by saying:  Show me where the
assertion occurs in the piece you ridiculed.  If you can't find it prepare
to admit that you are at least careless and at worst.....   Never mind, the
mind boggles....."

You said:

"The real way that needle valves work is by running "sonic", which refers to
the fact that the gas in the most tightly constricted part of the valve
reaches the speed of sound."

and

"To ensure sonic flow in either valve, you need the pressure drop to be
about 50% of absolute pressure.  If your output from the needle valve is a
couple of psi, this means an input gauge pressure of about 20psi to be safe.
Less and your valve will not be running sonic (possibly) and it may not be
providing the protection you are hoping for."

So, are you still insisting that "the real way a needle valve works" is only
when the gas running through it reaches the speed of sound?

TW

```