Avoid ball traps – Great Plains NP3000A Operator Manual User Manual
Page 111
Great Plains Manufacturing, Inc.
Maintenance and Lubrication
107
2014-04-22
407-613M
Avoid Ball Traps
IDLH Anhydrous Ammonia Exposure Hazard:
Beware of closed ball valves. A ball valve can trap liquid NH
3
.
If opened when disconnected, this liquid is likely at extreme
pressures, is emitted forcefully and vaporizes rapidly.
A 1
3
⁄
4
in ball valve can trap enough NH
3
to reach IDLH
a
vapor
concentrations, within moments, in a space the size of a two
car garage. Anyone present could be burned, blinded, or
receive serious or permanent lung injury. If this happens in an
enclosed space, the consequences could be fatal.
Refer to Figure 67
Always assume a closed ball valve contains liquid NH
3
under high pressure.
The flow gate of a traditional ball valve is a solid steel ball
with a hole through it. When closed, the hole cavity is
sealed by the side walls of the valve body.
If closed with the line full, the ball cavity is full of NH
3
.
If the valve is well constructed, that fluid remains there
indefinitely, presenting future field and service hazards.
Note: If the valve has a bleed valve and/or relief valve,
those safety valves do not vent the ball cavity when
a solid ball valve is closed. One of them may vent
just the downstream side of an orifice ball with the
ball closed.
The emergency shut-off valve
supplied on Great
Plains applicators in October 2010 and later has a relief
orifice on the downstream (strainer) side of the valve.
See note on page 14 regarding valve Warning decal.
Nurse tank hoses are likely to have solid ball valves
indefinitely. Treat all ball valves as potential traps.
▲ Wear your PPE
b
when servicing lines and fittings that are in
an uncertain status.
▲ Fully bleed all lines prior to servicing.
▲ Never carry a valve by the operating wheel or handle.
▲ Open ball valves when both sides of their lines are bled.
▲ Re-check the bleed on at least one side of the opened valve.
▲ If closing a ball valve for storage or parking, first wait for
the valve to warm to ambient temperature to ensure that no
liquid NH
3
remains.
▲ Never point a hose at your face.
▲ Treat all closed valves as possible traps.
▲ Never open a closed valve in an enclosed area. In addition
to the exposure hazard, a release of NH
3
could result in a
concentration level that is flammable or explosive.
▲ Never point a closed valve at your face.
▲ If replacing a ball valve, don’t just check that the new valve
is specified for NH
3
service:
Replace orifice ball valves only with orifice ball valves.
Replace solid ball valves with orifice ball valves.
▲ Install an orifice ball valve correctly. The orifice side points
down-stream (in the direction of flow).
a. IDLH: Immediately Dangerous to Life and Health
Figure 67
Legacy Valve Ball Trap
31614
Legacy Solid
Ball Valve
Newer Orifice
Ball Valve
Valve Open in Use
Valve Closed with
NH
3
Present
Lines Bled on Both
Sides of Valve
Valve Removed for
Service Still Closed
A18
b. PPE: Personal Protective Equipment