Great Plains NH3 Safety - Manual (Page 40)

36 NH
3
Safety Table of Contents Index Great Plains Manufacturing, Inc.
407-551M Table of Contents Index 2013-07-15
Use a Mirror
Refer to Figure 27
Blinding, Choking and Respiratory Hazard:
Never look directly into an ammonia hose or fitting.
Use a mirror. Always assume that ammonia is present in the
system. There are many ways it can hide, and surprise you
later. See “Avoid Trapped Anhydrous” on page 37.
Use a hand mirror to inspect hose ends, piping ends,
gaskets, vents and orifices.
About Bleed Valves:
Assume there is concentrated NH
3
at any bleed valve,
unless you are completely certain which segment of a
line is serviced by that bleed valve, and that the line
segment has been open to the atmosphere for some
time.
When installed on operating valves, it is not always
immediately obvious what the bleed valve protects.
On globe valves, a bleed valve near center-line might be
for venting upstream or downstream. On older ball
valves, a bleed valve near center-line might be for either
side, or even venting the ball cavity itself.
Refer to Figure 28
The purpose of a bleed valve is to perform a controlled
release, via an orifice
, of any fluid or gas trapped in a
closed line prior to operating other valves or uncapping
at a nearby Acme fitting.
If the line is discharged, opening the valve may have no
result, or may release a small amount of NH
3
vapor at
low pressure. Leave the valve open at the current
position. Move away up-wind. Return when the release
concludes.
If the line is not discharged, opening a bleed valve may
release NH
3
vapor at high pressure, or NH
3
liquid, most
likely as a spray.
If the there is liquid in the line segment, completion of a
bleed can take a long time. As the fluid turns to vapor, it
chills the remaining fluid, slowing evaporation.
Figure 27
Inspecting Fitting With Mirror
31565
Figure 28
Coupler Bleed Valve Detail
31569
Suffocation, Blinding and Burning Hazards:
Be up-wind when operating a bleed valve.
Wear chemical gloves when operating a bleed valve.
Wear goggles when operating a bleed valve.
Do not place your body or head in front of the orifice.
Follow a check-list when operating a bleed valve.
Open a bleed valve slowly.
Leave it open until all fluid and vapor flow ceases.
This can take a long time.
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