Advertisement
INSTALLATION
On liquefied gas systems, an external bypass valve, piped
back to the supply tank, is necessary for maximum pump
performance and longer pump life. The bypass valve must
be installed in the correct position on the discharge side of
the pump. (The word "IN" is cast on the inlet port of the
bypass valves.) The bypass valve will automatically prevent
excessive pressure resulting from accidental pump
overspeeding, discharge shut-off, or highly restrictive
receiving systems.
Correct installation and operation is essential. Service life is
enhanced by periodic inspection and careful maintenance.
Size the external bypass valve and its piping to
accommodate the full flow from the pump when the pump's
discharge line is closed and the pump is running at its rated
maximum speed.
When installing the external bypass valve, it is essential that
the pipe and fittings from the discharge port of the bypass
valve be sized properly. Excessive backpressure resulting
from friction loss in the bypass valve discharge piping will
cause a higher pressure than the actual bypass valve
setting.
For more information on sizing and friction loss, refer to the
Blackmer Liquefied Gas Handbook - Bulletin 500-001 (or
Bulletin 33 for other liquids) for pipe friction tables.
On liquefied gas systems, the external bypass valve
discharge must be piped back to the liquid or vapor
section of the supply tank never to the pump inlet. This
method of piping should also be used when pumping volatile
liquids from an underground tank or at high vacuum.
NOTICE
NEVER allow water or any corrosive product to enter
the Bypass Valve (e.g. for hydrostatic testing of
pipework). Severe internal damage may result.
If the Bypass Valve is not installed and commissioned
immediately, special preservative techniques will be
required. Low pressure nitrogen can be used to purge,
seal and protect the Bypass Valve from the effects of
condensation and atmospheric corrosion. Alternately a
¼ cup (60 mL) of diesel may be poured into the valve.
PIPING
The bypass valve should be installed
with the adjusting screw in the 12
O'clock (up) position. Mounting the
valve horizontally may cause
increased wear on the spool valve.
Flow must be into the port marked
"IN".
Remove pipe scale and other foreign
material such as PTFE tape residue
from the connecting pipelines. Apply
a suitable pipe thread sealant to the
male threads before fitting.
Never draw piping into place by use of
force at the port connections of the
Bypass Valve.
All piping should be supported
independently and line up accurately
with the Bypass Valve ports.
INSTALLATION
At temperatures below -20° F (-28.9° C) materials have
reduced impact strength. Provisions should be made to
prevent tools and other objects from impacting any
pressure containing components of the pumping system.
CHECKING THE EXTERNAL BYPASS VALVE
PRESSURE
1. Install a pressure gauge equipped with a needle valve or
snubber in the pump discharge gauge port.
pressure gauge on the tank and record the tank pressure.
2. Connect the delivery hose to the receiving tank.
3. Check all valves. The shut-off valve in the pump's discharge
line and the shut-off valve in the bypass return line should be
open.
4. Start pumping at the normal rate. Make sure the supply tank
outlet valve is wide open and check the direction of shaft
rotation to be sure it matches the direction of the arrow on
the pump.
5. To check the external bypass valve setting, gradually close
the shut-off valve in the pump's discharge line and record
the gauge pressure. The difference between this reading
and the tank pressure (before pumping) is the external
bypass valve setting.
6. For pumps with an internal relief valve (i.e., most PD pumps):
The external bypass valve must be set at least 25 psi (1.72
bar) less than the pump's internal relief valve setting.
To check the pump's internal relief valve pressure setting:
Gradually close the shut-off valve in the bypass return line.
Then slowly close the shut-off valve in the pump's
discharge line while watching the gauge pressure on the
discharge side of the pump. Record the peak differential
pressure (the difference between the discharge and inlet
pressure) when the internal relief valve begins to open.
NOTE: It is important to read the peak pressure just before
the pump relief valve opens. Once recirculation starts
through the pump relief valve, vaporization will cause the
pressure to fall quickly. For more information on the pump
relief valve settings and adjustments, refer to the
installation instructions for the specific pump.
After the internal relief valve setting has been determined,
reopen the shut-off valve in the pump's discharge line and
the shut-off valve in the bypass return line.
Hazardous pressure
can cause serious
personal injury or
property damage
551-E00
page 3/6
NOTICE:
External bypass valves shall be sized
and adjusted so the maximum pressure
of the system does not exceed the
lowest service pressure rating of any
component used in the delivery system.
Install a
Advertisement
