Liquid Controls V-7 Valves - Manual (Page 8)

8
V-7 Valves
Correct linkage adjustments avoid hydraulic shock.
Hydraulic shock occurs when a volume (mass) of liquid
moving at a high rate through a pipeline is stopped by a
valve that is suddenly closed. When the flow stops
abruptly, the mass of liquid acts as a battering ram,
causing a shock effect within the metering system. The
meter housing and internal parts receive the full impact
since the valve is located at the meter outlet. The greater
the mass, length of pipeline or velocity, the greater the
hydraulic shock and the greater the damage possibilities.
To prevent damage from hydraulic shock, a slow closure,
two-stage valve and preset should be used with the meter.
In some instances, mass, length of pipeline, or velocity
are of such a magnitude that using a two-stage valve is
ineffective. In this case, an impact absorbing, air
cushioning device should be used as an added
accessory.
The linkage between the valve and preset can be
adjusted to increase or decrease product flow during the
dwell period. To make adjustments shift the valve handle
to the slow flow or dwell setting. (See the preset counter
manual for more detail).
Turn the two 9/16 inch linkage nuts (Figure 14) located
on either side of the bracket to adjust the linkage for
proper dwell.
• On a right to left flow meter the nuts are moved to
the right to increase dwell flow and moved to the left
to decrease dwell flow.
• On a left to right flow meter the opposite is true.
Moving the nuts to the right decreases dwell flow
and moving nuts to the left increases dwell flow.
While adjusting the nuts, it is important to hold the linkage
rod firmly so that it does not move.
Proper adjustment is obtained when the far right wheel
of the preset counter (Figure 15) slows to a readable
rate and the characteristic dwell hiss is heard. Dwell
hiss is a low, resonating sound caused by slow moving
product through the valve.
When this is accomplished, tighten the adjusting nuts
ensuring that the linkage bracket is free to move, but
there is little slop between the linkage bracket and the
adjusting nuts.
Setting the Dwell
Figure 14: Linkage Adjustment
Figure 15: Preset Counter