Potable Water System Flashcards
When determining the level of a potable water hydro pneumatic header tank fitted with a tubular sight glass, what must be taken into consideration?
The actual water level in the hydro pneumatic header tank is identical to the level shown in the sight glass.
Suppose the pressure switch used to control the “lead” potable water pump is set at 45 psig cut-in for pump start and 55 psig cut-out for pump stop. What would be an appropriate setting for the “lag” potable water pump?
40 psig cut-in for pump start and 55 psig cut-out for pump stop.
To ensure potable water of drinking quality, chemical treatment is required for reverse- osmosis freshwater generators. What is the purpose of chemical pre-treatment?
Chemical pre-treatment sterilizes the sea water entering the unit to prevent bacteria from becoming resident in the reverse-osmosis unit filters and membrane modules.
Potable water pumps of the non-positive displacement type require…
…a vacuum-priming system if located above the potable water storage tanks.
On most commercial cargo vessels with a relatively small crew size and few users of the potable water system, how is the potable water system pressure maintained?
Cycling the potable water pump on and off by the action of the potable water hydro-pneumatic tank pressure switch in response to system demand changes.
What is the primary purpose of the lead-lag arrangement of the two potable water pumps supporting a typical potable water system?
Enabling the lead pump to cycle on and off during periods of relatively low demand and the lag pump to assist the lead pump only when the demand is high.
What design feature is used to minimize potable water wastage associated with hot water distribution piping for a potable water system?
Use of hot water recirculation loops.
Hot water heaters used in potable water systems may have multiple heat sources, such as an electric heating element and a jacket water heated tube bundle. What is the primary purpose of such an arrangement?
Allow electricity to be used in port and jacket water to be used while underway.
What are the operating characteristics of a “waterlogged” potable water system hydro pneumatic header tank that needs to be recharged with compressed air?
Very short and frequent running and idle periods for the potable water pump.
A constant pressure range is maintained in the potable water system of many vessels by using __________.
an air-cushion in the hydro-pneumatic tank
Distilled water from an evaporator may be discharged into a potable water tank through a…
solenoid operated three-way valve
The potable water pump is short cycling by the action of the pressure switch as a result of an unusually high level in the potable water hydro pneumatic header tank. What is most likely the cause?
The potable water hydro-pneumatic header tank is in need of recharging with compressed air due to absorption of air into the water over time.
