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850 and 950 Series
• Model 850: Pressure/Vacuum Relief Valve —
Pipe-Away
• Model 850/MVC: Marine Vapor Control System
Pressure/Vacuum Relief Valve. This product is fitted
with spark screens on the inlet and outlet ports in
accordance with 33 CFR Part 154
• Model 851: Top Mount Pressure or Side Mount
Vacuum Relief Valve — Pipe-Away
• Model 950: Pressure/Vacuum Relief Valve —
Vent-to-Atmosphere
• Model 951: Pressure Relief Valve —
Vent-to-Atmosphere
• Model 952: Top Mount Vacuum Relief Valve —
End-of-Line
• Model 952/MVC: Marine Vapor Control System
Vacuum Relief Valve
• Model 953: Side Mount Vacuum Relief Valve
Smart Wireless Monitoring Option
The Smart Wireless Monitoring Option is available
with PVRV Models 850 (Pipe-away) and 950
(Vent-to-atmosphere). This option allows the remote
sensing and "OPEN/CLOSED" value transmission
of the open or closed status of the pressure vent,
the vacuum vent or both. Use Option Code WP for
pressure vent monitoring, Option Code WV for vacuum
vent monitoring or WPV for the monitoring of both at
the end of the model string. Knowing whether a PVRV
is open or closed can enable immediate response
to prevent problems related to safety, emissions and
quality of the tank contents.
The following are a few specific examples of how this
added visibility can help prevent problems:
Example #1 – Redundant PVRV's
Redundant PVRV's are commonly used for added
safety. If the primary PVRV fails closed or partially-
closed, then the backup PVRV automatically takes
over. This is achieved by establishing a pressure set
point that is slightly higher for the backup device. In
this way, if the primary PVRV fails, the tank remains
protected. But redundancy is lost and should be
addressed as soon as possible. But how will you
know if this has occurred? Monitoring the open/
closed position of the backup PVRV can provide quick
identification of this issue, for either the pressure or
vacuum side. Under normal conditions, the backup
PVRV remains closed. If the backup PVRV is open,
this points to either the primary PVRV not functioning
4
as expected or a separate pressure control problem
in the tank system that is causing both PVRV's to
be open. Ideally, the wireless monitoring of both
primary and backup devices is preferred in order to
gain the most insight. Further troubleshooting can
then be performed and the problem can be detected
and addressed.
Example #2 – Tank Blanketing
Tank blanketing is sometimes used in order to inert
the vapor space in a tank for added safety. A tank
blanketing regulator controls the inflow of nitrogen
or another blanketing gas by responding to a low
pressure set point. In this scenario, a PVRV (vacuum
side) generally acts as a backup to the blanketing
regulator. If the blanketing system fails for some
reason, the PVRV automatically takes over, as its
set point is slightly higher than that of the regulator.
But once again, how is one to know that this has
occurred? A wireless-monitored PVRV would indicate
that the vacuum side is open. Under normal operation,
it should be closed.
Example #3 – Emergency Vent
A storage tank's emergency vent should remain
closed, except in abnormal conditions. If an
emergency vent is also remotely monitored, and found
to be open, then there may be a pressure control issue
somewhere in the system. In this scenario, the PVRV
should also be open. If it is not, it could be part of the
issue. Again, a wireless-monitored PVRV can readily
provide this information.
Product Identification and Marking
Hazardous Locations
Enardo pressure/vacuum relief valves are available
with outer housings of carbon steel, stainless steel or
aluminum, as indicated in Figure 5.
Nameplate
A nameplate is attached to the valve and contains the
following information:
• Model Number – Ex. VALVE, 950-8-10X
• Conn. Flange Size and Rating – Ex. 4 in.
• Serial Number
• Tag Number (Optional)
• Notified Body Number – Ex. 2460
• Cat. No. (Category Number) –
Ex. II 1 G c T6 or II 2 G c T6
• Year – Ex. 08
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