Subject: Re: [TR] What is the correct way to measure fuel pressure

From: Chad <[email-masked]>
Date: Mon, 21 Oct 2019 18:45:35 +0000 (UTC)

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 Was the pump running?
    On Monday, October 21, 2019, 01:42:47 PM CDT, Sujit Roy <triumphstag@gm=
ail.com> wrote: =20
=20
 I borrowed a Harbor Freight fuel=C2=A0pressure gauge from a fellow Triumph=
 owner. I disconnected the supply to the ZS carbs and connected the pressur=
e gauge directly to the feed.The gauge read less than 1 PSIG. I have a Stag=
 and it is using an SU electric fuel=C2=A0pump.The stag pump should=C2=A0be=
 around 3 psi.=C2=A0Am I measuring the pump correctly? Should I Tee in the =
gauge inline with the carbs instead?
Sujit

--=20
Sujit Roy
Cupertino, California
https://triumphstagblog.wordpress.com/

** [email-masked] **

Archive: http://www.team.net/pipermail/triumphs  http://www.team.net/archiv=
e

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<html><head></head><body><div class=3D"ydp31631a6dyahoo-style-wrap" style=
=3D"font-family: Helvetica Neue, Helvetica, Arial, sans-serif; font-size: 1=
3px;"><div></div>
        <div dir=3D"ltr" data-setdir=3D"false">Was the pump running?</div><=
div><br></div>
       =20
        </div><div id=3D"ydpd9ba2c34yahoo_quoted_2632488465" class=3D"ydpd9=
ba2c34yahoo_quoted">
            <div style=3D"font-family:'Helvetica Neue', Helvetica, Arial, s=
ans-serif;font-size:13px;color:#26282a;">
               =20
                <div>
                    On Monday, October 21, 2019, 01:42:47 PM CDT, Sujit Roy=
 &lt;[email-masked]&gt; wrote:
                </div>
                <div><br></div>
                <div><br></div>
                <div><div id=3D"ydpd9ba2c34yiv8388298803"><div dir=3D"ltr">=
I borrowed a Harbor Freight fuel&nbsp;pressure gauge from a fellow Triumph =
owner. I disconnected the supply to the ZS carbs and connected the pressure=
 gauge directly to the feed.<div>The gauge read less than 1 PSIG. I have a =
Stag and it is using an SU electric fuel&nbsp;pump.The stag pump should&nbs=
p;be around 3 psi.&nbsp;</div><div>Am I measuring the pump correctly? Shoul=
d I Tee in the gauge inline with the carbs instead?</div><div><br></div><di=
v>Sujit<br><div><br></div><div><br clear=3D"all"><div><br></div>-- <br><div=
 dir=3D"ltr" class=3D"ydpd9ba2c34yiv8388298803gmail_signature"><div dir=3D"=
ltr"><div>Sujit Roy<br>Cupertino, California</div><div><br><a href=3D"https=
://triumphstagblog.wordpress.com/" rel=3D"nofollow" target=3D"_blank">https=
://triumphstagblog.wordpress.com/</a><br><br></div></div></div></div></div>=
</div></div>** <a href=3D"mailto:[email-masked]" rel=3D"nofollow" =
target=3D"_blank">[email-masked]</a> **<br><br>Donate: <a href=3D"=
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From: Sujit Roy <[email-masked]>
Date: Mon, 21 Oct 2019 11:46:51 -0700

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Yes, it was.

On Mon, Oct 21, 2019 at 11:45 AM Chad <[email-masked]> wrote:

> Was the pump running?
>
> On Monday, October 21, 2019, 01:42:47 PM CDT, Sujit Roy <
> [email-masked]> wrote:
>
>
> I borrowed a Harbor Freight fuel pressure gauge from a fellow Triumph
> owner. I disconnected the supply to the ZS carbs and connected the pressure
> gauge directly to the feed.
> The gauge read less than 1 PSIG. I have a Stag and it is using an SU
> electric fuel pump.The stag pump should be around 3 psi.
> Am I measuring the pump correctly? Should I Tee in the gauge inline with
> the carbs instead?
>
> Sujit
>
>
>
> --
> Sujit Roy
> Cupertino, California
>
> Donate: http://www.team.net/donate.html
> Unsubscribe/Manage:
> http://autox.team.net/mailman/options/triumphs/[email-masked]
>

-- 
Sujit Roy
Cupertino, California

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<div dir=3D"ltr">Yes, it was.=C2=A0<br></div><br><div class=3D"gmail_quote"=
><div dir=3D"ltr" class=3D"gmail_attr">On Mon, Oct 21, 2019 at 11:45 AM Cha=
d &lt;<a href=3D"mailto:[email-masked]">[email-masked]</a>&=
gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0=
px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div>=
<div style=3D"font-family:&quot;Helvetica Neue&quot;,Helvetica,Arial,sans-s=
erif;font-size:13px"><div></div>
        <div dir=3D"ltr">Was the pump running?</div><div><br></div>
       =20
        </div><div id=3D"gmail-m_5767127872895906384ydpd9ba2c34yahoo_quoted=
_2632488465">
            <div style=3D"font-family:&quot;Helvetica Neue&quot;,Helvetica,=
Arial,sans-serif;font-size:13px;color:rgb(38,40,42)">
               =20
                <div>
                    On Monday, October 21, 2019, 01:42:47 PM CDT, Sujit Roy=
 &lt;<a href=3D"mailto:[email-masked]" target=3D"_blank">triumphstag=
@gmail.com</a>&gt; wrote:
                </div>
                <div><br></div>
                <div><br></div>
                <div><div id=3D"gmail-m_5767127872895906384ydpd9ba2c34yiv83=
88298803"><div dir=3D"ltr">I borrowed a Harbor Freight fuel=C2=A0pressure g=
auge from a fellow Triumph owner. I disconnected the supply to the ZS carbs=
 and connected the pressure gauge directly to the feed.<div>The gauge read =
less than 1 PSIG. I have a Stag and it is using an SU electric fuel=C2=A0pu=
mp.The stag pump should=C2=A0be around 3 psi.=C2=A0</div><div>Am I measurin=
g the pump correctly? Should I Tee in the gauge inline with the carbs inste=
ad?</div><div><br></div><div>Sujit<br><div><br></div><div><br clear=3D"all"=
><div><br></div>-- <br><div dir=3D"ltr"><div dir=3D"ltr"><div>Sujit Roy<br>=
Cupertino, California</div><div><br><a href=3D"https://triumphstagblog.word=
press.com/" rel=3D"nofollow" target=3D"_blank">https://triumphstagblog.word=
press.com/</a><br><br></div></div></div></div></div></div></div>** <a href=
=3D"mailto:[email-masked]" rel=3D"nofollow" target=3D"_blank">triu=
[email-masked]</a> **<br><br>Donate: <a href=3D"http://www.team.net/do=
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=3D"nofollow" target=3D"_blank">http://www.team.net/pipermail/triumphs </a>=
 <a href=3D"http://www.team.net/archive" rel=3D"nofollow" target=3D"_blank"=
>http://www.team.net/archive</a><br><br>Unsubscribe/Manage: <a href=3D"http=
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[email-masked]</a><br></div>
            </div>
        </div></div></blockquote></div><br clear=3D"all"><div><br></div>-- =
<br><div dir=3D"ltr" class=3D"gmail_signature"><div dir=3D"ltr"><div>Sujit =
Roy<br>Cupertino, California</div><div><br><a href=3D"https://triumphstagbl=
og.wordpress.com/" target=3D"_blank">https://triumphstagblog.wordpress.com/=
</a><br><br></div></div></div>

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From: Sujit Roy <[email-masked]>
Date: Mon, 21 Oct 2019 11:48:10 -0700

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I could hear the pump ticking then it stopped. That's when I read the gauge.
Sujit

-- 
Sujit Roy
Cupertino, California

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<div dir=3D"ltr">I could hear the pump ticking then it stopped. That&#39;s =
when I read the gauge.<div>Sujit</div></div><br><div class=3D"gmail_quote">=
<div dir=3D"ltr" class=3D"gmail_attr">On Mon, Oct 21, 2019 at 11:46 AM Suji=
t Roy &lt;<a href=3D"mailto:[email-masked]">[email-masked]</a=
>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0px=
 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><di=
v dir=3D"ltr">Yes, it was.=C2=A0<br></div><br><div class=3D"gmail_quote"><d=
iv dir=3D"ltr" class=3D"gmail_attr">On Mon, Oct 21, 2019 at 11:45 AM Chad &=
lt;<a href=3D"mailto:[email-masked]" target=3D"_blank">triumph74tr6=
@yahoo.com</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=
=3D"margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding=
-left:1ex"><div><div style=3D"font-family:&quot;Helvetica Neue&quot;,Helvet=
ica,Arial,sans-serif;font-size:13px"><div></div>
        <div dir=3D"ltr">Was the pump running?</div><div><br></div>
       =20
        </div><div id=3D"gmail-m_-3703624473927350220gmail-m_57671278728959=
06384ydpd9ba2c34yahoo_quoted_2632488465">
            <div style=3D"font-family:&quot;Helvetica Neue&quot;,Helvetica,=
Arial,sans-serif;font-size:13px;color:rgb(38,40,42)">
               =20
                <div>
                    On Monday, October 21, 2019, 01:42:47 PM CDT, Sujit Roy=
 &lt;<a href=3D"mailto:[email-masked]" target=3D"_blank">triumphstag=
@gmail.com</a>&gt; wrote:
                </div>
                <div><br></div>
                <div><br></div>
                <div><div id=3D"gmail-m_-3703624473927350220gmail-m_5767127=
872895906384ydpd9ba2c34yiv8388298803"><div dir=3D"ltr">I borrowed a Harbor =
Freight fuel=C2=A0pressure gauge from a fellow Triumph owner. I disconnecte=
d the supply to the ZS carbs and connected the pressure gauge directly to t=
he feed.<div>The gauge read less than 1 PSIG. I have a Stag and it is using=
 an SU electric fuel=C2=A0pump.The stag pump should=C2=A0be around 3 psi.=
=C2=A0</div><div>Am I measuring the pump correctly? Should I Tee in the gau=
ge inline with the carbs instead?</div><div><br></div><div>Sujit<br><div><b=
r></div><div><br clear=3D"all"><div><br></div>-- <br><div dir=3D"ltr"><div =
dir=3D"ltr"><div>Sujit Roy<br>Cupertino, California</div><div><br><a href=
=3D"https://triumphstagblog.wordpress.com/" rel=3D"nofollow" target=3D"_bla=
nk">https://triumphstagblog.wordpress.com/</a><br><br></div></div></div></d=
iv></div></div></div>** <a href=3D"mailto:[email-masked]" rel=3D"n=
ofollow" target=3D"_blank">[email-masked]</a> **<br><br>Donate: <a=
 href=3D"http://www.team.net/donate.html" rel=3D"nofollow" target=3D"_blank=
">http://www.team.net/donate.html</a><br>Archive: <a href=3D"http://www.tea=
m.net/pipermail/triumphs" rel=3D"nofollow" target=3D"_blank">http://www.tea=
m.net/pipermail/triumphs </a> <a href=3D"http://www.team.net/archive" rel=
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bscribe/Manage: <a href=3D"http://autox.team.net/mailman/options/triumphs/t=
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.net/mailman/options/triumphs/[email-masked]</a><br></div>
            </div>
        </div></div></blockquote></div><br clear=3D"all"><div><br></div>-- =
<br><div dir=3D"ltr"><div dir=3D"ltr"><div>Sujit Roy<br>Cupertino, Californ=
ia</div><div><br><a href=3D"https://triumphstagblog.wordpress.com/" target=
=3D"_blank">https://triumphstagblog.wordpress.com/</a><br><br></div></div><=
/div>
</blockquote></div><br clear=3D"all"><div><br></div>-- <br><div dir=3D"ltr"=
 class=3D"gmail_signature"><div dir=3D"ltr"><div>Sujit Roy<br>Cupertino, Ca=
lifornia</div><div><br><a href=3D"https://triumphstagblog.wordpress.com/" t=
arget=3D"_blank">https://triumphstagblog.wordpress.com/</a><br><br></div></=
div></div>

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From: "Randall" <[email-masked]>
Date: Mon, 21 Oct 2019 14:12:04 -0700

Don't forget to account for the difference in height between the pump and
carbs.  The spec in my book is 2.7 psi measured at the pump; and if I've
done my math right, each 3.75" rise will reduce that by 0.1 psi.  So
assuming the carbs are about 2' above the fuel pump, you should see closer
to 2 psi at the carb inlets.

But I don't trust measuring tools from HF, especially used ones.  Check it
with another gauge; or if you don't have one, build a simple manometer.  A
6' length of pipe or tubing could make a simple "go/no-go" gauge; hold it
vertically and if the pump can push fuel out the top, you've got enough fuel
pressure.  Or for temporary use, some cheap vinyl tubing from Home Depot
tied to a piece of wood will let you read the height.  Vinyl isn't rated for
fuel of course, but should do for a quick test.  (Don't use it for anything
else afterwards, though.)  37.4" should equal 1 psi of gasoline (using
numbers I got from Google).

Not at all relevant, but the book also calls the pump "high pressure", which
I find amusing.

-- Randall 
56 TR3 TS13571L once and future daily driver
71 Stag LE1473 - awaiting engine rebuild
71-2-3 Stag - awaiting gearbox rebuild 

> I borrowed a Harbor Freight fuel pressure gauge from a fellow 
> Triumph owner. I disconnected the supply to the ZS carbs and 
> connected the pressure gauge directly to the feed.
> The gauge read less than 1 PSIG. I have a Stag and it is 
> using an SU electric fuel pump.The stag pump should be around 3 psi. 
> Am I measuring the pump correctly? Should I Tee in the gauge 
> inline with the carbs instead?

---

From: Michael Porter <[email-masked]>
Date: Mon, 21 Oct 2019 21:22:40 -0600

> to 2 psi at the carb inlets.

Umm, this might confuse a couple of principles.  Yes, lifting a column 
of liquid by atmospheric pressure limits the column to 34 feet (of 
water, or the equivalent), and the figures above reflect that for the 
lower density of gasoline.  But, the fuel system is not pumping against 
atmosphere.  It's a closed system (at least when the float valve is 
closed), and with the gauge directly connected to the fuel line, it's 
definitely a closed system from pump outlet to gauge.  And, by 
definition, the gauge reads PSIG, i.e., pressure above atmospheric, 
regardless of ambient air pressure.

In a closed system, pressure equalizes at all points in the system, so, 
2.7 psi at the pump would be 2.7 psi at the gauge.

That said, taking the measurement might be time-dependent due to the 
construction of the pump.  It may build to the correct pressure and then 
quickly leak down past the pump inlet check valve.  Dunno about the 
construction of this pump.  But, leaving the ignition in the "on" 
position while taking the reading and keeping it on to determine if the 
pump is building to rated pressure, then shutting off and leaking down 
would be advisable. If peak pressure never gets above 1 psig, then the 
pump's defective and needs replacement or rebuilding.

> numbers I got from Google).

I generally agree with the comment about measuring tools from HF, 
especially if one does not know the percent error at full travel. And, 
if one doesn't know the extra energy required to move the needle off 
zero (overcome inertia), it gets more complicated, especially for 
measurements on the low end of the scale.

As for the manometer, yes, a handy way to verify pressure, and in that 
case, because the tube is open to atmosphere, all the above comments 
about height of the column apply.

> Not at all relevant, but the book also calls the pump "high pressure", which

As compared to gravity feed, perhaps?  :)

Cheers.

-- 

Michael Porter
Roswell, NM

Never let anyone drive you crazy when you know it's within walking distance....

Unsubscribe/Manage: http://autox.team.net/mailman/options/triumphs/[email-masked]

---

From: "Randall" <[email-masked]>
Date: Mon, 21 Oct 2019 21:02:15 -0700

> Umm, this might confuse a couple of principles.  Yes, lifting 
> a column of liquid by atmospheric pressure limits the column 
> to 34 feet (of water, or the equivalent), and the figures 
> above reflect that for the lower density of gasoline.  But, 
> the fuel system is not pumping against atmosphere.  It's a 
> closed system (at least when the float valve is closed), and 
> with the gauge directly connected to the fuel line, it's 
> definitely a closed system from pump outlet to gauge.  And, 
> by definition, the gauge reads PSIG, i.e., pressure above 
> atmospheric, regardless of ambient air pressure.

True, but regardless of whether there is atmosphere on top, the pressure
goes down as you get higher along a column.  In effect, the weight of the
fuel (or whatever) inside the column is sitting on top of the pressure at
the bottom, so pressure goes down as you go up.

> 2.7 psi at the pump would be 2.7 psi at the gauge.

I disagree.  If, for example, you set up the system I suggested with a 6'
length of pipe, 2 psi at the bottom and no fuel coming out the top; then you
plug the top with a pressure gauge, the pressure does not magically increase
just because there is a plug there.  The gauge still reads 0 psig.

Normally, this effect is too small to notice, because we work with much
higher pressure in hydraulic systems.  3 or 4 psi in a system that works at
hundreds of psi (like a clutch) doesn't make enough difference to notice.

-- Randall

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