subbase. The pump shaft shall be constructed of corrosion resistant alloy
steel, sleeve bearings and glands of bronze designed to accommodate a
mechanical seal. Pumps shall have stainless steel impellers and casings of
bronze. The motors shall have sufficient power for the service required,
shall be of a type approved by the manufacturer of the pump, shall be
suitable for the available electric service and for the heat transfer fluid
used, and shall conform to the requirements specified in Section 16402
INTERIOR DISTRIBUTION SYSTEM. The motors shall be controlled by suitable
switches that can be activated by either the differential temperature
controller or by manual override (Hand-Off-Automatic). Each pump suction
and discharge connection shall be provided with a pressure gauge as
specified.
2.7.3
Pipe insulation and coverings shall be applied in accordance with Section
15080A THERMAL INSULATION FOR MECHANICAL SYSTEMS as called out for steam
piping to 103 kPa 15 psig. Array piping insulation shall be capable of
withstanding 121 degrees C 250 degrees F, except that piping within 450 mm
1.5 feet of collector connections shall be capable of withstanding 204
degrees C 400 degrees F.
2.7.4
Expansion Tank
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NOTE: Care should be taken by the designer to
properly size the expansion tank according to the
guidance in TM 5-804-2. This expansion tank sizing
criteria requires the expansion tank to be able to
accept an amount of fluid equal to the fluid volume
of the collectors plus piping at the same height or
above the collectors. This is in contrast to the
conventional method of sizing the expansion tank to
account for thermal expansion of the heat transfer
fluid. The method described above allows for the
large volume increase corresponding to the
vaporization of fluid in the collectors during
stagnation. This "oversizing" provides a fail-safe
means of system pressure control during stagnation
conditions, and prevents heat transfer fluid
discharge by keeping the system pressure below the
maximum 862 kPa (125 psig) relief value. A
bladder-type expansion tank is required to separate
the heat transfer fluid from the metal tank
material. Use of a precharged tank allows the
overall tank size to be smaller. Care should be
taken to ensure that the expansion tank precharge
pressure is less than the fill pressure at the
expansion tank. Items to be shown on the drawings
must include:
a. Expansion tank acceptance and total volume
b. Expansion tank and bladder materials
c. Maximum relief, system cold fill, and precharge
pressures.
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Expansion tank shall be constructed and tested in accordance with ASME BPVC
SEC VIII D1 and as applicable for a working pressure of 862 kPa 125 psig.
SECTION 13600A
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