Chromalox PQ410-4 - Manual (Page 3)

Note: If the expansion tank cannot be mounted above the highest
point in the system, or if the system is going to operate above the
boiling temperature of the heat transfer fluid, the expansion tank
will have to be pressurized with air or nitrogen. This eliminates the
possibility of heat transfer fluid flashing into vapor in the heater,
at the point of high velocity in the system or at the suction of the
pump which will cause the pump to vapor lock due to insufficient
NPSH (net positive suction head). On hot oil heat transfer systems,
this pressurizing is usually done with nitrogen as this eliminates
the possibility of the hot fluid coming in contact with oxygen thus
reducing the possibility of oxidation, extending the life of the heat
transfer fluid. This pressure should be 5-10 PSI above the vapor
pressure of the heat transfer fluid at its operating temperature. DO NOT pressurize expansion tank or system unless proper safe-
ty relief valves are provided.
WARNING: If expansion tank is to be pressurized,
then it must be equipped with safety relief valve(s).
If this pressure exceeds 15 PSIG, then the heat
transfer system and expansion tank should be
ASME coded.
DO NOT mount expansion tank directly on top of system unless
absolutely necessary. If mounted on system, provisions must be
made for cooling of the expansion tank line. Maximum safe oper-
ating temperatures are reduced when expansion tank is mounted
on system unless positive suction pressure of 2 to 3 psig is main-
tained on pump.
-3-
6. EXPANSION TANK LOCATION
7. SYSTEMS MOUNTED ABOVE PROCESS EQUIPMENT
(Ceiling or Platform mounted)
8. PUMP ALIGNMENT
9. PUMP PACKING ADJUSTMENT
Pumps with packed stuffing box or seals may require adjust-
ment during system start up. Packed seals are designed to leak
some oil for proper lubrication of the pump shaft. Drip pans and
drain connections are provided on these pumps to contain the oil
and allow convenient removal.
Packed pumps will frequently leak oil at start up until the sys-
tem reaches operating temperature and the seals seat on the shaft.
When system reaches temperature, tighten the two packing gland
nuts evenly, approximately
1 /
4
turn at a time until the shaft seal
leaks 1 to 2 drops per minute. Do not overtighten or shaft damage
will occur.
Note: If normal oil leakage from a packed pump is unacceptable
in the application, mechanical seal pumps are available at extra
cost. Contact factory.
When mounting system above process equipment, check to be
sure the pump will not be vapor locked. The cause for vapor lock
is insufficient NPSH (net positive suction head). This problem is
particularly prevalent on systems with centrifugal pumps, but also
can appear on systems with positive displacement pumps. The
things to check when a system is mounted above the process
equipment are as follows:
A. Piping: Eliminate all unnecessary turns and restrictions in the
return piping which could cause a vapor lock.
B. The expansion tank should be connected into the pump suction
line and be located high enough to create the necessary NPSH
(See No. 6). If the expansion tank cannot be elevated then it
should be pressurized with air or nitrogen to obtain the neces-
sary NPSH. This will create a positive head on the pump and
prevent the heat transfer fluid from flashing into vapor at the
pump suction when the system is operating at temperatures
equal to or exceeding the vapor temperature of the heat trans-
fer fluid.
DO NOT allow pump to hammer or cavitate. Excessive vibration
will damage pump and may break pump castings.
CAUTION: All pump and motor mounts and motor-belt should be
checked and tightened if necessary. These sometimes loosen dur-
ing transit.
Belt Driven — The belt has been properly aligned and adjusted
for the proper deflection prior to shipment from the Chromalox
factory. The proper deflection is
1 /
4
”.
Direct Coupled — The pump and motor on each Chromalox heat
transfer system is factory aligned prior to shipment. However, as
recommended in our instruction sheet on each particular heat
transfer system, the pump and motor could become misaligned in
transit and therefore, should be realigned in the field after the unit
has been permanently set in place. Misalignment can cause wear
on the pump shaft, packing or mechanical seal and bearings. It will
cause excessive stuffing box leakage and will eventually cause
complete failure of the pump and in turn, the system.
To check alignment:
A. Place a straight edge across the coupling, it should be in full
contact with both rims at the top, bottom and both sides. Rotate
coupling by hand and repeat this check.
B. Check the ends of the meshed teeth on the coupling jaws with
a feeler gage. The ends of the teeth should be equidistant
around the circumference of the coupling. Do not rotate shaft
when making this check. Allowance must be provided for
pump shaft and motor shaft expansion.
Figure 1