Red Jacket LPG Premier, Руководство по установке, Страница: 19 / 40

Introduction System Protection
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When the temperature of LPG increases, it can vaporize. Vaporized liquefied petroleum gas expands at a rate of
approximately 265:1. Due to the liquid vaporizing, sections of the LPG pump staging wear and will be damaged.
The motor of the pump needs to be cooled. Red Jacket does this by using the LPG. When operating, the LPG
runs through and around the motor to cool it. In addition, LPG is used to lubricate the bearings. The first impeller of
the pump needs to be submersed, so that the LPG can cool the motor. If the product level is too low, the motor
cannot cool itself and the bearings will not be lubricated. Eventually the motor will fail.
When the pump is installed in a manifold another potential problem may occur. The equalization line is important to
balance the liquid levels in the tank and the manifold. As stated above, the LPG cools the motor. Hence, some of
the warmth of the motor is transferred to the LPG. Through the internal by-pass approximately 20 liters/min. (5.2
gallon/min.) will be pumped back in to the manifold. If, for any reason, the equalization line does not operate well,
the liquid in the manifold can warm up. Consequently, the pressure in the manifold increases and, because of a
higher-pressure level in the manifold compared to the tank pressure, all the liquid can be forced back in the tank,
emptying the manifold. With the pump running, this is also a form of dry run.
Low-pressure/Dry-Run Protection Unit (LPG Run Box)
Red Jacket LPG pumps must be installed in accordance with the minimum requirements and it is to be
recommended to include in the installation a so-called Low-pressure/Dry-Run protection unit (preferably based on
pressure technology.) When installed according to the specifications, the pump will perform for many years.
When a pump fails it is mainly due to one of two events: cavitation or dry run. Veeder-Root does not warrant these
two failures. The LPG Run Box is a safety device available for the Red Jacket submersible LPG pump that is
designed to avoid cavitation and dry run of the unit.
The LPG Run Box is a differential pressure based system. When cavitation is about to occur, the pump cannot
build up differential pressure. Similarly, with a dry run the pump cannot build up pressure as well. Basically, the
LPG Run Box constantly receives pressure information of the total system and with this data it ‘chooses’ to stop or
start the pump. A pressure transmitter is needed to send this information to the LPG Run Box. A pressure
transmitter is thus a vital device of this system.
Since the LPG Run Box controls the pump, the LPG Run Box sends a signal to start the pump when a nozzle is
picked up. Immediately, the pressure in the discharge line is compared to the vapor (or rest) pressure. If the
differential pressure is greater than 100 kPa (14.7 psi) the system is OK. During operation, the LPG Run Box
continues to check the differential pressure. The differential pressure needs to be above 400 kPa (58.9 psi). If the
pressure falls below this given set point the LPG Run Box will turn the pump off. The pump is being protected from
low pressure and low liquid level/dry run (no differential pressure). The system automatically restarts, but if the
differential pressure continues to remain outside the working range, it stops and sounds an alarm.