Author Topic: Check valve in 1957 fuel pump ?  (Read 3845 times)

Offline Bill Balkie 24172

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  • 1957 Biarritz / 2009 CTS
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Check valve in 1957 fuel pump ?
« on: September 05, 2011, 05:37:39 AM »
 I have installed a Carter auxiliary fuel pump in my car for quick starts after siting for awhile and for insurance just in Car my mechanical pump fails .  I run 100% of the time on my Mechanical pump . The electric pump is installed back by the fuel tank and is controlled by a push / pull switch under the dash .  The two fuel lines are independent and  come together  both entering a Y fitting( the other feed from the Mechanical pump ) at a fuel bowl , then off to the carburetor .  My question is .... does  the stock Mechanical pump   have a built in check valve  to insure gas will not flow backwards when the auxiliary Electric pump is pumping ?  The last thing i want to do is pump my crank case full of fuel .  I was thinking it might not be a bad idea installing an check valve on the outlet side of the Mechanical fuel pump anyway .  Thanks Bill
Bill Balkie
1957 Biarritz
2009 CTS


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Re: Check valve in 1957 fuel pump ?
« Reply #1 on: September 05, 2011, 09:10:15 AM »
there should be a poppet valve in the pump that closes when the pump pushes fual out the outlet side of the pump.
i do not believe thus would hold the pressure from an electric pump constantly hammering it
if the valve fails ,fuel will be returned to tank via fuel feed line
if the diaphram fails ,then you will fill engine with gas
also now the fuel pressure from the stock pump has somewhere else to go beside the carb and will return to tank via new line hose you installed.feeding pressure to the outlet side of an electric pump cant be good for that pump either.

it only takes a small amout of gas in the oil(any you may not even detect it in time) to ruin an engine as the washed out oil will not lubricate properly

i am not sure the reasoning behind running the electric pump as a back up but i personally would remove or byass the mechanical pump and run the electric 100%
i think there are now too many connections to fail or leak and the more surface area near the engine the greater chance for heating up the fuel
i recently bypassed the pump on my 1962 caddy and it works great

Offline R Sotardi #11719

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Re: Check valve in 1957 fuel pump ?
« Reply #2 on: September 05, 2011, 12:10:56 PM »
I'm curious, what type electric pump are you using on your 62 ?

Offline Bill Podany #19567

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Re: Check valve in 1957 fuel pump ?
« Reply #3 on: September 05, 2011, 03:16:15 PM »
Please inform me: if gasoline gets into the engine will it ruin the main bearings?  How does one know if fuel is backing into the engine.  I have a parallel fuel line system from the tank engaging the electric fuel pump, and it has a check valve in the line.  Will this prevent gasoline from backing into the engine?  I am mechanically without merit, so I appreciate the insight.

Bill Podany
Knoxville, TN
1941 60 Special Fleetwood
1955 Eldorado


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Re: Check valve in 1957 fuel pump ?
« Reply #4 on: September 05, 2011, 03:43:59 PM »
Bill P
where is the check valve? in original line or new line

it seems like a lot of work to run a separate fuel line for the electric pump
just curious as why so many people install a electric to feed a mechanical one

if you back feed a mechanical pump, the poppet valve may not hold pressure and fuel will return to tank,
if diaphram in fuel pump has too much fuel in mechanical pump, trying to pump while full pressure, diaphram may rupture
chances i think are pretty low but they exist.
i personally would never feed a mechanical pump with a electric pump, too much work also to run complete separate line too, im lazy and look for simple solutions to my problems
if you have run a second line already, i take it you are not too worried about %100 originality anyway
i would rather have a not quite original car i can use than a original one i cant trust or use

i just run the electric pump.
you can remove the stock fuel pump pushrod and leave lines and pump in place if you so choose, but do not recomment running fuel through a disabled pump for reasons above,
i moved the fuel line from the front of the engine to the firewall away from the heat and ran in the carb from the backside and completely removed my mech pump
no more vapour lock of extended cranking because the fuel has boiled out of the carb from a hot shut down
turn on key,wait a few seconds and turn the key

electric pumps do fail as do mechanical ones,but a failed electric pump will not allow fuel in the engine through a failed diaphram
ethanol does a nice job eating many components,old rubber diaphrams is one of them
ethanol eats fiberglass and some plastic boat tanks, floats, carb inners etc
will try to post picture later
of a second pump i just bought for my old ford bronco

i run a carter vane pump
carquest #E84070
carter #4070
no regulator required ,at least on my car
has 5.5 psi and plenty of fuel volume

Offline Bill Balkie 24172

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  • 1957 Biarritz / 2009 CTS
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Re: Check valve in 1957 fuel pump ?
« Reply #5 on: September 05, 2011, 06:01:20 PM »
62 droptop ,
   No one is running an  electric  pump to feed a mechanical pump. Simple stated we are running two independent pumps with lines that feed the fuel filter  before the carburetor .  I had my mechanical pump fail on me about 100 miles from my house one day . All i have to do now is pull a switch and my Carter   rotary Pump will kick in and it does not feed through  the mechanical pump .

 My original question was does the mechanical pump have a check valve , so gas can not inter Through  the outlet  side of the pump ?

 also with the Carter pump I can get a quick shot of gas into my Carburetter after the car has been sitting for a few weeks .
Bill Balkie
1957 Biarritz
2009 CTS


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Re: Check valve in 1957 fuel pump ?
« Reply #6 on: September 05, 2011, 08:15:52 PM »
there will be a poppet valve of sorts in the fuel pump,one on inlet side and one on outlet side
when diaphram creates a vacuum the outlet one closes and the inlet one opens
there should be a small spring to assist in closing valves
when the diampham compressed the fuel, the inlet valve closes and the outlet one opens ,both due to pressure
i am not sure how much pressure the outlet valve will handle as it was not really meant to handle out side pressure forcing against it when the electric pump is on .
it was meant  to handle the residual pressure in the line to the carb and stop that fuel from returning to pump, but a constant pressure may find its way by

fairly easy to check out, remove the inlet line from the mechanical pump and turn on the electric one and see if anything comes out
repeat the process with the engine running after the inlet to the pump has been removed to stop new fuel from being introduced
you can purchase a electric solenoid lock off to install in either fuel line if you are worried about back feeding
i would think the mechanical pump would also be feeding back through the electric as it is still part of the equal pressure in all directions closed circuit when the engine is running

sounds like most people are running the similiar carter vane  pump

another  reason i replaced my mechanical pump was the new ones made now are junk
i went through 4 or 5 to find one that actually worked properly
even then,it was a year old when i changed it and i noticed the main actuating arm pivot pin had worked its way out of the casing about 60% ,so it was just about to fail anyway

i see how you have the pump plumbed in now, just do not understand why you didnt just run the straight electric and save the trouble of running a second fuel  line.
it is nice to be able to prime the carb with the electric pump, specially when car  has sat or is hot




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Re: Check valve in 1957 fuel pump ?
« Reply #7 on: September 05, 2011, 08:21:37 PM »
forgot to mention, the easiest way to check for fuel in your engine oil is to pull the dipstick and smell the oil
when oil has been used a while it will smell,but if there is gas in it it will really smell
also good idea to change oil if engine has been badly flooded as fuel will bypass rings and end up in engine oil

had a carb issue on my old truck ,just after i change oil,8qts full synthetic plus additive ,around $60 of brand new oil wasted as was now washed out with gas as float needle and seat failed to seat and flooded engine

Offline Bill Balkie 24172

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Re: Check valve in 1957 fuel pump ?
« Reply #8 on: September 05, 2011, 08:29:56 PM »
62 droptop,
    The next time My mechanical pump give me trouble i think i will take your advise and run the Electric pump and bypass the Mechanical pump , I also have a carter 4070 installed by the tank , i am a toolmaker by trade and made a bracket to mount the pump onto the frame about 12 inches from the fuel tank . I have found the carter  rotary pumps to be very noisy . But on the other hand they are very dependable .

 Thanks Bill
Bill Balkie
1957 Biarritz
2009 CTS


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Re: Check valve in 1957 fuel pump ?
« Reply #9 on: September 05, 2011, 10:11:29 PM »
i agree the carter are kind of noise,but so are other brand rotary pumps
i just took apart my old mechanical pump and inspected the check valves
they are mearly a rubber washer backed by a weak spring
if you have access to and know how to use machines it should be no problem for you to install a bypass pipe in the pump housing so you can run fuel right through the housing,use it for looks and hose junction just like original
on my current mechanica pump, twice the poppet valves (whick are an assemble pressed into the housing)decided to come out of their location
i was able to pin point the problem and have the car back running in less than 15 minutes both times with only a screwdriver on hand to repair, i actually used the tire iron as a hammer to pein the housing a bit to stop the valve from falling out again
when i took it apart again tonight ,the outlet valve was cock eyed and looks like it was on the move out again
they dont make parts like they used to
i can post pictures of the internals if any one is interested

w lee

Offline Glen

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Re: Check valve in 1957 fuel pump ?
« Reply #10 on: September 06, 2011, 02:18:38 AM »
Maybe a review of how a mechanical fuel pump works will help.

The mechanical fuel pump has a diaphragm, a spring that forces it into the pump chamber, a lever that is operated by a lobe of the cam shaft that will force the diaphragm in the opposite direction, and two check valves usually of the poppet type. 

When the cam lobe comes around the lever pulls the diaphragm out of its chamber causing a low pressure.  The low pressure draws fuel in from the inlet line opening the check valve.  After the lobe of the cam has passed the spring presses on the diaphragm to force the fuel out the outlet check valve and closing the inlet check valve.  The strength of the spring and the surface area of the diaphragm regulate the pressure at the outlet check valve. 

If the carburetor is not using fuel fast enough the diaphragm just hangs there slowly supplying fuel as needed to the carb.  The next time the cam lobe comes around the lever only pulls the diaphragm just enough to reset it to full stroke.  There will be a short negative pressure pulse when this happens pulling in a little more fuel. 

The more fuel the carb is using the more fuel the pump supplies up to the total displacement of the pump.  But remember the more fuel used the faster the engine runs the more often the cam bumps the diaphragm.

If you add an electric fuel pump to the system, things change depending how it is connected and its outlet pressure. 

If the electric pump is simply added to the fuel line on the input side of the mechanical pump it will push fuel through the mechanical pump and push the diaphragm back.  If the outlet pressure of the electrical pump is higher than the mechanical pump the diaphragm will be pushed back and the lever on the cam will not pull it any further.  Fuel pressure at the carb is the outlet pressure of the electric pump. 

If the electric pump has a lower outlet pressure it will still push fuel through the mechanical pump and the diaphragm will be bumped by the cam and lever as needed.  Fuel pressure at the carb will be regulated by the mechanical pump. 

If the pumps are connected in parallel (like Billís) the fuel pressure at the carb will again be the higher of the two pumps. 

The pressure on the outlet check valve of the mechanical pump will be the difference between the two pumps (positive or negative).  The pump with the lower pressure will be idle. 

One additional thing at some point and I am not sure when that happened the mechanical pump were equipped with a weep hole.  This hole is located so that if the diaphragm leaks the weep hole will keep the leaking fuel out of the crankcase.  But it is only about an 8th of an inch in diameter so it will not take a large flow and can be plugged by dirt. 


Glen Houlton CLC #727 
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Offline StevenTuck

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Re: Check valve in 1957 fuel pump ?
« Reply #11 on: September 06, 2011, 05:35:51 AM »
After reading the subject of an electric fuel pump several times, I put a call into a local restoration shop I have used. The foreman has been working on these cars all his life. The first question he asked me is why would I install an electric fuel pump. He stated that the main reason these pumps fail is because owners don't drive their cars enough. He said he does not install an electric fuel pump as a normal thing.

I guess I am a purist and don't mind the longer start after sitting several weeks. It is really not that long...maybe 15 seconds. Are we all in such a rush in our lives that we can't wait 15 seconds.

The restoration shop foreman said that as long as you operate the car on a regular basis you should not have a problem with the mechanic fuel pump.

By the way, your shop manual should have a diagram of the fuel pump assembly. There are inlet and outlet check valves. The inlet allows gas into the fuel pump from the tank. The oulet sends gas to the fuel bowl and then to the carburetor. If you have Air Conditioning on your car there should be a return line to the pump from the filter bowl.
1962 Cadillac Eldorado Biarritz
Car Show Signs and Car Photo Books


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Re: Check valve in 1957 fuel pump ?
« Reply #12 on: September 06, 2011, 07:22:53 AM »
the reason i installed an electric pump on my car is because i was getting tired of cranking my car for a minute or so after it cooled down from a hot shut down
the fuel would boil in the carb and evaporate
i have pulled top off fuel pump after a hot shut down after it cooled, the pump was completely dry, and i blocked the inlet line to rule out syphoning from the inlet side check valve when i first shut it down
the fuel pump on the 62 is in such a brilliant place, highest point possible next to all the heat
i am not in a rush to start the car,
i do not want to take out the starter from all the cranking required ,not to mention at a car show having to crank the beast forever to start
the modern fuel with all its non gas stuff in it boils around 140-150 degrees f
the fuel is not going into my crank case and my carb is not leaking down
if i park it cold ,i can come back 3 or 4 weeks later ,hit the pedal once and it starts instantly
shut it down hot,different story
in the last 2 years or so,all my carbbed v 8's have suddenly developed this issue
electric pump on all 3 took care of the problem, and all 3 did have good functioning mechanical pumps
Shell touts new nitrogen enriched fuels, means less gas and more air
ethanol same thing,less pure gas and more crap

Glen good analogy of the mechanical pump, it is truely a variable displacement pump based on demands

try for gas stations around the country that sell pure no additive gasoline

Offline StevenTuck

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Re: Check valve in 1957 fuel pump ?
« Reply #13 on: September 07, 2011, 05:48:09 AM »

I am sorry you had or are having misfortunes with your fuel delivery system. I call it fuel delivery system because there are many components to getting the fuel to the carburetor besides just the fuel pump. You obviously are having an issue and it seems the electric pump has resolved it for you. However, I don't believe it is the pump.

I have a 1962 Cadillac and having been running on the stock factory fuel delivery system including stock fuel pump since my car has been restored 20,000 miles ago. I do have air conditioning and the fuel delivery system has a return line from the fuel filter bowl back to the tank.

I don't have the problems you are experiencing. My car does take about 15 seconds to start if it has sat for several weeks. It always starts up immediately after reaching operating temperature.

I do add MARINE STA-BIL to my fuel at each fillup, one ounce to each 10 gallons. I also use premium fuel. Wikipedia, the free encyclopedia, states: "A higher octane rating allows a higher compression ratio, and thus higher temperatures and pressures, which translate to higher power output. When gasoline is not stored correctly, gums and solids may accumulate resulting in "stale fuel". Fuel stabilizers can be used to extend the life of the fuel that is not or cannot be stored properly. Fuel stabilizer is commonly used for small engines, such as lawnmower and tractor engines, to promote quicker and more reliable starting. Run an engine for ten minutes to circulate the stabilizer through all components prior to storage, and to run the engine at intervals to purge stale fuel from the carburetor.

The key to trouble free operation: 1) operate your vehicle regularly 2) use a stabilizer 3) use premium fuel 4) keep your engine operating temperature below 200 degrees.

Good luck.
1962 Cadillac Eldorado Biarritz
Car Show Signs and Car Photo Books


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Re: Check valve in 1957 fuel pump ?
« Reply #14 on: September 07, 2011, 05:29:43 PM »
Steven, being a mechanic for the past 25 years i have seen many issues arise with fuel systems ,
i realize the issue i had may have been cured by a new mechanical pump, but having been through 3 pumps in the last 7 years i didnt feel like gambling again
the entire system is in good working order, all hoses are new, the sending unit is like new, the lines have been vacuum tested for leaks and all ok
the carb is like new, does not leak down as i can leave fuel in it for a couple months and it is still there when i start it up, as long as it was parked with a cool engine
when my car is warmed up , in summer heat ,it will start instantly as long as it has not sat for a 1/2 hr or so which is just enough time to boils the carb and pump empty
days under low 70's temp  out never really been an issue ,just the hot days
now with electric pump, even when parked hot,i let the pump run for 10-15 seconds and it starts like a dream,everytime,just like it should

it is possible,that when your car was restored they were still making quality replacement pumps, the newer ones, not so much

i do drive my car a lot, i will think nothing of going for a recovery mission with a trailer in tow returning with another prized vehicle, or even atrip to the city dump with a trailer of junk in tow
last week i hauled a fairly lark wood chipper trailer to buddies cottage 35 miles away 
i have on many ocasions done over 1300 miles on a weekend and do not have time for a fuel pump let down again
i only use high test gas when i  1 , towing with the car or
                                                  2 i am going to be playing hard with it want
                                                     all the ponies awake   
i use fuel stabilizer only when i put away for the winter and wont be started for a couple months
the only time regular octane gas was an issue is when i was climbing some big hills on the interstate and it was pinging a bit passing a car up hill

my car is non a/c and does not have the return line
that may be the main reason you do not have as big of a problem as the boiling vapours have somewhere to go 
thanks for the thoughts and suggestions

Offline Renato

  • 1957 Cadillac Fleetwood- restoring cars, restoring leathers
  • Posts: 217
Re: Check valve in 1957 fuel pump ?
« Reply #15 on: November 26, 2011, 08:23:32 AM »
I'm using my factory mechanic fuel pump. I never use not factory parts like electic fuel pump etc... My system works great. The only bad point if tha car sitting for longer time the diaphragm does not hold the gas.  I do not know why  not fitted a manual section for the fuel pump. Every old europian car have. I will check my feasibility. I think I will use a vave between the carburator and the fuel pump. It allow the gas, but hold it.

I have an 57 De Ville 4 door.
R. Bognar


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