[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: Ball valves

> Date: Tue, 11 Jun 2002 14:18:32 -0700 (PDT)
> From: john wheeler <jcwheel76 at yahoo_com>
> Subject: Ball valves
> Hey gang,
> I was at my friendly neighborhood compressed gas
> dealer, and we got to talkin shop a little. I'm
> currently on the market for a needle valve manifold,
> and he showed me something neat.
> He described it as a "ball valve" and said that it
> should give a *little* better control than a needle
> valve. It is a brass "Y" with 2 control knobs. They
> would be very easy to link together to get as many
> outlets as I wanted, and the price would blow away
> anything I've found for sale from aquarium
> retail/e-tailers. Plus, I like the brass fittings
> instead of the nylon that I've been using.
> Has anyone ever used these or heard of it? I'm trying
> to find a reason to not get it;) I'm not very
> comfortable doing this stuff DIY.
> TIA,
> John Wheeler

A needle valve uses a needle and a seat made to match the contour of the
needle to control flow.  A ball valve uses a ball with a hole drilled
through it for the flow control.  In the closed position the hole
through the valve is perpendicular to the flow path and so the sides of
the ball block off both the inlet and the outlet to the valve.  As the
valve is opened a part of the hole through the ball becomes open to the
inlet and outlet.  When fully open the hole is collinear with the flow
path and there is no restriction in the flow path as you have with most
other types of flow control devices.  

The ball valves I have seen only have a 1/4 turn adjustment from fully
closed to fully open.  With only a 1/4 turn, there is little precise
control of the effective orifice and thus little precise control of the
flow.  If you size it properly (fully open Cv or Cp small enough to be
in the range you need) I suppose it is possible to get what you need in
flow control.  My education is in electronics and some controls so I do
not have a great understanding of all practices nor all that is
available in the area of flow control.  However, I thought that ball
valves were most commonly used to provide more of an on/off control than
a metering control and that one should use a metering valve (needle
valve) for a more precise metering of the quantity of flow.

Many home and garden shops have ball valves like this for use with
garden hoses.  Obviously these are much larger than what you will need
for a CO2 system but you can see how they work.  Better Homes and
Gardens makes such a ball valve exclusively for WalMart that is an
inline device (not a 'Y') which clearly shows how these work.