[modeleng] Re: Singing Injectors
- From: "Phill Smith" <steam@xxxxxxxxxxxxxx>
- To: <modeleng@xxxxxxxxxxxxx>
- Date: Tue, 22 Mar 2005 23:26:27 +0800
IP,
Any given injector doesn't feed the same amount of water at different
pressures. Nor do will it feed the same amount of water at the same
pressure. The reasons why, are many. But the main 2, are, feed water
tempurature and throttling of the water supply. An increase of the feed
water tempurature requires more water to be supplied to the injector so as
to allow opperation at the correct temp'. If you don't, then it will start
spitting steam and water from the bypass, as there will not be enough water
flowing to condense the quantity of steam being supplied (it absorbs too
much of the heat being supplied). This effect is why injectors DON'T work
above it's maximum design temp'. This is also what happens if you throttle
back the feed water too much.
If it is supplied more water than "optimum", it will stop "singing", start
to drip/dribble, and lower the temp' of the water being discharged. While it
will still maintain a flow, the delivery pressure will drop dramatically,
and it will cool the boiler down faster (and hence increase the thermal
stesses in the area around it's entry to the boiler). If you continue to
increase the over supply of feed water to the injector, it will of course
fail from not having absorbed enough kinetic enery from the steam to lift
the check valve, and hence simply run profusely from the overflow.
Now with all the information what does it mean???? Simply this. Ideally you
want to supply only enough water for it to run dry (no discharge at all from
the overflow), as this will feed the boiler with the hottest posible water
for the amount of steam being used. It is also when it is opperating at peak
efficiency. It also happens to be when the injector is "singing". Once it
starts to "chirp", you know it is either getting too much or not enough
water. Injectors have the avantages (over other forms of boiler feed
devices) of supplying hot (approx 75°C) water to the boiler (when operating
at optimum) with no moving components. The delivery water temp' limit is
just over 80°C, so you can see in the design stage, we walk a fine line.
This is because the hotter the water supplied to the boiler, the less energy
is taken form the water already in the boiler that we are trying to boil to
create steam. It will feed more water than optimum, but that is not the
objective.
Cheers,
Phill.
----- Original Message -----
From: "Pendragon" <idpriest@xxxxxxxxxxxxxxxx>
To: <modeleng@xxxxxxxxxxxxx>
Sent: Tuesday, March 22, 2005 1:03 AM
Subject: [modeleng] Re: Singing Injectors
> Jessie,
>
> I am no expert but as I say I don't believe they should sing, from =
> personal
> observation it does appear though that my injectors fill the boiler up
> quicker when used as I describe rather than when they are having a good
> sing. I appreciate that there is a very fine line between singing and
> working as I've suggested.
>
> Regards, IP
>
> Priest & Sons Model Engineers
> http://www.kinvermes.pwp.blueyonder.co.uk/p1.htm
>
>
> -----Original Message-----
> From: modeleng-bounce@xxxxxxxxxxxxx =
> [mailto:modeleng-bounce@xxxxxxxxxxxxx]
> On Behalf Of JESSE LIVINGSTON
> Sent: 20 March 2005 12:14
> To: modeleng@xxxxxxxxxxxxx
> Subject: [modeleng] Re: Injectors
>
>
> Pentagon,
>
> I never thought of it that way. Next time I have one of my injectors
> running I will have a look-see at the overflow. I always figured the =
> happy
> little sound was the steam combining with the water on its way through =
> the
> injector. Sort of like the frying sound that steam bubbles make just =
> before
> the water starts to boil in a boiler or stew pot on the stove. I know I =
> have
> heard the exact same singing sound come from the injector on a full size
> traction engine.
>
>
> =20
>
> --=20
> No virus found in this outgoing message.
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> =20
>
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>
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