A few College questions

[joe brown]

Hello everybody, Im just doing a mock theory test at college and im stuck on a few questions because we havent covered them yet, Its preparing us for the exam in two weeks. Can you help.

1. Which of the following is the correct type of joint that can be used to make a connection between two sections of polybutylene hot water pipe?

a] Push fit
b] End feed capillary
c] Capillary solder ring fitting - i think its this one
d] fusion welded fitting

2. which of the following can be used to overcome the problems with long dead legs in hot water systems pipeworks.

a] Apply trace heating
b] Apply localised cooling
c] Fit a shock arrestor
d] Fit a non return valve

Now i was thinking that you would fit a pump and create a secondry circulation - But that isnt there so am i correct in thinking Non return valve?

3. Which of the following types of copper tube would normally be used to form the cold feed pipe to a hot water storage cylinder.

a] R220 minibore coils
b] R220 soft coils - i think it is this
c] R250 half hard lengths
d] R290 hard lengths

4. the maximum working pressure of a copper hot water pipework system is 0.4 bar. What is the soundness test pressure to be applied to meet water regulation requirements?

a] 0.2 bar
b] 0.4 bar
c] 0.6 bar
d] 0.8 bar

5. What is the minimum gap required in a feed and expansion cistern between the finished (heated) water level and the invert level of a warning pipe

a] 10mm
b] 25mm
c] 50mm - i think it is this
d] 100mm

 

[migoplumber]

post your answers first, then you might get a few more replies !!

 

[macplumb]

1. A
2. A
3. C
4. C
5. C

 

[billybongo]

Trace heating to a dead leg has got to be wrong , surely

 

[macplumb]

A dead leg can have 2 meanings. 1 a long run to a draw off
2 a run that had been capped off and no longer use. As the regs state these should be cut out to stop water stagnating and forming leginella. This is also known as a dead end.
I belive the problem the question is getting at is heat loss. So I would say the answer is trace heating.
What would you say the answer is and why? Cheers

 

[joe brown]

Sorry, My answers are - well the first one is plastic pipe so obviously its pushfit - why i couldnt think of that is beyond me..lol ,

Question 2 , i havent a clue, as i state in the original post i assumed you would insert a pump on a low flow setting just to create a secondry circulation. They are talking about wastige of hotwater in a dead Leg pipe.

As for the rest i havent a clue - thats why i asked

why would you have trace heating in a dead leg???

 

[plumbitearth]

Number 1 is A
Number 2 will have a look but looks like as per the answer macplumb gave
Number 3 is C
Number 4 C i think
Number 5 is C

 

[billybongo]

Macplumb, if i am honest i dont know the answer , but deadlegs are non moving water as you said so to heat it up in my mind would accelerate bug growth , the nrv seems more logical because it would not allow that leg of water back .

 

[andyg0507]

A
a
c
c
d

did this test last week on smart screen and didnt get any of the above wrong.

 

[macplumb]

But if can get a nrv in you would Cut back cap off and leave the leg empty leaving no risk of bacteria growing. See what I mean.

 

[billybongo]

Yes i agree if the leg is no longer used its a cut back as close as poss to flowing water , but if its in use i cant understand trace heating , we need a mind with the definitive answer

 

[joe brown]

I was under the im pression that a dead leg is a long piece of pipe that is not part of the circuit and causes wastige of hot water. What i mean is they try to keep the pipe as short as possible to the first tap, Otherwise the water in the pipe would cool down and be wasted. If i was to turn the hot tap on i would waste water waiting for the hot water to arrive from the cylinder as it would be cold first..then when i shut the tap off the remaining water in the pipe would also be wasted as it would go cold!

They are talking about preventing this - so trace heating possibly would keep the water heated

 

[helpsy]

A
A
C
C
B
I think I was taught :-
Redundant length of pipe= dead end
Excessive run of hot supply with long draw off until water reaches required temp= dead leg.
I may be wrong though thats how I interpretted it.( requiring bronze pump etc, secondary circulation)

 

[andyg0507]

joe if you are at college you could always have a word with your tutor and get him to set your smart screen account up for you, all the answers to your questions are on there.

give it a go.

 

[joe brown]

Helpsy i agree with you, i was taught the same regarding dead end and dead leg!!

 

[WaterTight]

I was in college a year and a half ago and the answer is trace-heating. But it was an answer my tutor made a point of saying was not one of City and Guilds finest moments. There were plenty of things he told us he didn't agree with on the exams. But you have to pass the exams so that's the answer you put. Secondary circulation and pumps are what most plumbers would do. And by dead leg they mean any pipe run, in use, between the heated water source and the appliance.

 

[Plumbstar Tom]

As far as im aware a dead leg is a run of pipe that contains water when a terminal is turned off

Say a hot feed to a shower is 10m in lenghts. When the shower is off this wter is cold and useless and has to run through the shower until hot water can fill it

This is known as a dead legs

I may be wrong though

 

[TGor]

But if can get a nrv in you would Cut back cap off and leave the leg empty leaving no risk of bacteria growing. See what I mean.

You guys are not reading the question ..

which of the following can be used to overcome the problems with long dead legs in hot water systems pipeworks.

a] Apply trace heating
b] Apply localised cooling
c] Fit a shock arrestor
d] Fit a non return valve

Its an exam not reality!! you can use trace heating to keep the "dead leg" (i.e. a long pipe to a fixture without a secondary return) at usable temperature! This avoids wastage of water.

 

[WHPES]

I remember being told by tutors "You've got to do it this way for City and Guilds but the rest of the time you must do it this way instead as this is the industry standard"

Can't remember anything at the moment except using lead clips for securing flashings on the City and Guilds course, which is not recommended anymore in industry.

 

[stevetheplumber]

I remember being told by tutors "You've got to do it this way for City and Guilds but the rest of the time you must do it this way instead as this is the industry standard"

Can't remember anything at the moment except using lead clips for securing flashings on the City and Guilds course, which is not recommended anymore in industry.

what do the reccomend now then ?

 

[heinz57]

1) a
2) a
3) c
4) c
5) b

 

[WHPES]

Here's an interesting calculation I remember from college - how to calculate the heat loss from different diameter copper pipes.

Heat transfer coefficient - Wikipedia, the free encyclopedia


The equation here is how you work out the rate of heat transfer for the copper tube within the cylinder and hence determine what overall length it must be for a certain rate of heat transfer (in watts). To work out in BTU, divide by 3.414 :

Heat transfer coefficient - Wikipedia, the free encyclopedia

You can also use the same equation to calculate heat losses from insulated and uninsulated pipe.