M a i l Bag
Mail Bag
Responses to past articles
b y G e o r ge Lan t h i e r
I
I mentioned purges, pre and
post and I'll come back to that. I also mentioned my
dislike for check valves and here's what I said, "NEVER
put check valves in oil systems, they should not be used
anywhere in any oil system. They are more trouble looking
for a spill to happen and it will happen and I have the legal
files to prove it! At the top of the system (booster) you need
a vacuum breaker, but never a check valve. A good well
designed, properly piped and leak free system doesn't need
them, only people who don't know how to pipe and cut
flares use them. I know that's cold and cruel but read every
single book you can find from pump OEMs, none show
check valves… hmmm."
Well, a lot of people didn't like that and a couple even asked
me to prove it about check valves. Well, I could go on and on
but let me just quote a couple of sources I consider indisputable. The first is the SUNTEC Installation and Service Manual
from Suntec and it's available at www.suntecpumps.com. From
the Suntec Manual, "A properly installed fuel oil heating
system does not require check valves for proper operation."
Now keep in mind this takes in a lot of pumps since Suntec
makes Beckett's Clean-Cut and designed Riello's Mectron - 40
- Gulliver - RDB pump.
n a past article about boosters
Second, from the WEBSTER Service Tech Handbook available from www.websterfuelpumps.com, and again I quote "Check
valves must be oil tight. Low pressure drop swing type are recommended to minimize friction loss."
A-ha, so it turns out I wasn't 100 percent right, but I was
a long way from wrong, too, because if you go through those
books, you won't find a drawing showing check valves. Suntec
just doesn't believe in them and Webster only calls them out
when their Model 48598 Vacuum Breaker is used as "an in line
check," Figure 1.
The situation has to do with Cv or the flow coefficient or the
flow capacity rating of a valve. It turns out that most of us who
might use a check valve don't use a low Cv swing checks on oil
lines and booster systems that are of the swing type, Figure 2.
What most of us use are the high Cv ball-spring checks, Figure
3, and that's the problem. With many ball-spring check designs
you could have a high Cv valve that adds as much as two inches of
Mercury(Hg) to the job and to open the valve, Figure 4. If you're
at design or close to it, there goes the ballgame. By using a low
Cv valve or the more commonly called "flapper check," Figure 5,
you create less restriction and less vacuum. Webster Pumps does
make a vacuum breaker that has a low Cv and it can be used as
an inlet check, Figure 1.
Figure 2
Figure 1
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April 2013 | FUEL OIL NEWS | www.fueloilnews.com
