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21 Cards in this Set
- Front
- Back
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2 reasons for installing a control valve on the cold supply to the hot water tank |
To turn of water to tank, And to isolate hot water supply to repair faucets and replace washers |
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Why must cold water always enter near the bot of the tank |
To ensure cold water doesn't mix with hot waterwhat |
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What is purpose of sacrificial anode |
Reduce corrosion due to electrolysis |
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Why are gas and electric tanks heavily insulated |
For min heat loss |
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What coatings may be applied to the steel tank to prevent corrosion |
Galvanized coating, glass or stone lining |
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Why is t and p req on a hot water tank |
Prevent hwt from exploding due to water flashing to steam and the resulting 1700 times expansion in vol |
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2 advantages of electrical tank |
Quiet, more choice of location because no flue |
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Name 4 npc codes that apply to hwt installation |
1. Cold water shut off close to tank 2. T and p located within 6" of top of tank 3. Device to shut off electricity when water reaches temp 4. Every pipe that conveys water from a t and p or other relief valve must meet specified req |
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What size should the discharge pipe from a and p valve be |
Same size as inlet |
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Where should the outlet terminate |
No more than 12" or 300mm |
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What alteration may be made to a t and p valve |
None |
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What device is installed to prevent a hot water tank from exploding |
T and p valve |
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What is meant by thermal lag on a hot water tank |
In desirable time req to wait for hot water at faucet outlet |
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What can be done to prevent t and p valve from liming up |
By using plastic coating on sensing elements and installing t and p valve on vert pos |
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At what temp do fusible Plugs melt |
210 F |
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How should t and p valve be sized |
According to burner input rating |
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2 styles of electric tanks |
Immersion type element, strap on elements |
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Diff bet immersion and strap on elements |
Immersion has the element in the water in the tank. Strap on has the element on the exterior of tank |
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Main disadvantage of instant hot water heater |
Input req with freq short draws of hot water |
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Recommended water temp for domestic use |
60 C 140F |
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How is siphoning from tank protected |
A small hole called an anti siphon is drilled into the top of the dip tube at the inlet |
