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Comprehending proportional valves

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Comprehending proportional valves

Postby MMamdouh » Sun Apr 05, 2009 11:36 am

this topic is for discussing the concept of proportional valves and what modifications can be done to change their characteristics... the ultimate goal of this post is to know what changes should be done to OEM P valves whenever a brake upgrade is done either on the front or rear brakes.

i will put it in four main points to help me understand the concept and requirements involved and also avoid confusing you guys during the process... the main three points are:

1- my understanding to what P valves do
2- my understanding to how P valves do what they are supposed to do
3- my findings regarding OEM p valves on our daewoos
4- the required modifications to OEM P valves given the rear disk conversion and what parts of the P valves are involved

First part:

This is what i understand as far as P valves go... in the simplest definition, they are used to decrease the brake pressure going to the rear wheels from the one going to the front... this is done simply because the rear tires are more vulnerable to lockup under braking due to weight shift and locking the rear can cause a car to spin out of control thus we must have the appropriate rear brake pressure that will allow the front to lock before the rear.

from the research i have done on the internet i found many topics but this one is the most informative:

http://www.stoptech.com/tech_info/wp_pr ... lves.shtml

now this article shows that their are two characteristics for a P valve... and that is the knee point and the slope, knee point is the point where proportioning starts, the slope is the ratio of proportioning between front and rear... so simply it is "when" and "how much".

By all means feel free to correct me if i go something wrong.

Second part:

this is my understanding to how P valves actually works... after dismantling the OEM P valve of a lanos i found out it consists of a ported valve, spring and a spring loaded plastic part... i suppose the big spring is the one responsible for the location of the knee point on the graph since a spring is sensitive to pressure and as far as i understand it will compress at some point changing the brake fluid passage and thus start restricting the pressure so spring power is related to the knee point.

the size of the port in the valve itself is deciding the slope of the curve after the knee point... since port sizes and all affects pressure in a circuit so i suppose the bigger the port the less slope angle you will get (if the valve was totally blocked you would get zero pressure to rear after knee point)

Third part:

i have found out that Dewoos have two different P valves... i was at the mechanic's shop during the rear brakes conversion and found out the following:

1.5 Lanos P valves are marked 3/40 while 1.6 Lanos and Nubira P valves are marked 3/30... no idea what does them numbers refer two, i have dismantled both valves and found out that both internal valves have the same port ( i didn't have a measurement tool to do so and i relied on my eyes... if their was a difference then it will be very very minimalistic) so as far as i understand both valves got the same slope after the knee point.

the major difference i saw was the spring... they both got the same thickness but the 3/30 valve got a longer spring than the 3/40 one so as far as i understand i suppose it is applying more pressure on the valve thus creating a different knee point and the 3/30 valve that has the longer spring have a higher knee point than the 3/40 valve

Fourth part:

the rear brake upgrade for my car involved dual piston rear calipers with needs more work from the brake master to move the bigger pistons... i suppose this translates to "higher knee point" thus i should be using the 3/30 valve springs or even stronger springs to elevate the knee point to compensate for the bigger volume of fluid required at the rear

as for the slope... i have no idea what i should have... :roll: :roll: :roll:

should i have more sloping as the rear disk setup is supposed to be stronger and more vulnerable to lockup?
Should i have less sloping as i still suffer from the big volume requirement after the knee point as well?
Should i keep it as it is as the knee point adjustment is enough to handle the big volume requirement yet the rear setup is not that powerful to lock the rear anyways?

i know this is rather confusing and will require some testing for various setups but at least i want to know which rout i should go with first to avoid testing a thousand possible combinations so I'd like some theoretical analysis and advice from you guys to have a plan for testing

and again this is my current understanding to fluid pressure and P valves so i might be wrong in one or more areas here so please correct me whenever i am wrong

MMamdouh
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Re: Comprehending proportional valves

Postby wolfsreign » Thu Apr 23, 2009 3:33 am

if im reading and paying attention to the dates right, you have already did your brake swap.

um.. i have not that much of a clue, but offer my brain power.. for me i would use trial and error for the last 2 options.. but i wouldnt want to lock up the back what so ever when im doing 60+mph on city streets.. @.@ ive spun out of control many many times already. bent a few rims in the process and a few A-frames by jumping curbs lol. :oops:

anyway... i would say try doing a weight ratio thing.
meaning compare your cars front and rear weight to the other cars that you are thinking of using the valves and/or master cylinders.
(yes i understand that the rear does have two valves (i think you said valves or was it pistons. forgot.).)

my other idea would be seeing if you could get specs on the calipers. like the pressure needed to move it 1mm.. or whatever.

so like figure out the measurement of (x)kpa/1mm for the new two piston (one caliper would be easiest then trying to figure out two)
then get the measurement of your front. (get where im going?) {b.c im so confused in my head right now. haha too tired}
then basically they will both be the same distance from the rotor, so now you can compare the pressure they both need.

so i guess lets have an example. the (stock) front wheels lock up at 1,000psi
and the rear since they have two valves lock up at 1,200psi..
i would let the "p valve"? put alittle more pressure on the backs then the fronts since it takes more. but at the same time, this is where i think my first idea of the weight comes into play..
b.c the two valve (new ones) need more pressure b.c the weight was more intense in the back of the old car..
but im guessing your car has less weight in the back than the old car, you should leave the pressure equal as the backs dont have all the old weight. so then they wont lock up.


ill stop there.. and see if anyone could like summarize or refine my scattered logic.
basically compare and contrast the cars (your car to the donor car.)
~wolf
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Re: Comprehending proportional valves

Postby MMamdouh » Mon Apr 27, 2009 7:35 am

i did some testing on Thursday

first off... my car is the only 1.5 SOHC with 3/30 P valves... no idea how did it get their (i am the third owner) but anyways this is good since i already upgraded the front braking system so i am on the correct valves... but this means i only have one option: mess with the port on the P valve as i already have the stiffer spring

i have took off my P valves and replaced the ported valves with the ones i modified and did some brake tests...

i didn't notice any rear lockup on dry tarmac.. even when braking in corners... non of the rear wheels locked
on sand covered tarmac i have developed rear lock... and that scared me indeed... had to call my good friend Bob3825 to join in the testing process and give me a second opinion.

Bob was watching me driving and braking progressively on sand and he confirmed that the rear did lock... but it locks AFTER the front locks and that is good news as from what i heard the problem is in locking the rear before the front as that will cause a non controllable spin.

actually i have managed to spin the car under braking but that was circumstantial as the front tires were on clean tarmac while the rear was on the sandy tarmac and i was going to the left... the rear locked before the front and the car spun but hat was at some 20 KPH or something so it was not a scary moment.

the only problem is that i am not sure how much difference did the ported valves do to braking as i didn't test the rear lockup before changing the valves... anyways i think the current status is good enough to live with

MMamdouh
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Re: Comprehending proportional valves

Postby wolfsreign » Tue Apr 28, 2009 5:50 am

well since im gonna be doing the same as you in due, i guess ill go the 3/30 too, as im rolling the 1.6 DOHC and that's prob like <20lbs extra weight.
anyway how do you tell what the valve is? does it have markings on it?
and whats on ur front? drilled? slotted? (if i remember correctly you said you replaced them with bigger ones(wider)?
and at the same time, what are the backs? drilled? slotted?
~wolf
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Re: Comprehending proportional valves

Postby MMamdouh » Tue Apr 28, 2009 8:45 am

since you already have the 1.6 DOHC lanos then you already have the 3/30 P valves... the ratio is engraved on the body of the P valve itself and it is easily viewable

the modification that you "might" need is drilling the valve inside the P valve assembly if you are not getting enough rear braking power... i suggest you do the rear disk conversion then test the car with the P valves untouched, if you can lock the rear after the front on low grip surface then you don't need to do any modifications... if you can't then you will need to drill the ports on the P valves to 1mm or so then repeat the test

as for my car... i have a 1.5 SOHC and that comes with 236mm front rotors and those are not good at all for a car of that weight... given the fact that their is only 20 Kgms weight difference between the 1.5 SOHC and 1.6 DOHC... i simply upgraded my front brakes to the 1.6 DOHC lanos specs... and i have done so on a couple a friend's cars as well

viewtopic.php?f=3&t=9527

viewtopic.php?f=3&t=10969

Image

their were plans to get EBC's slotted and dimpled rotors but their are some issues between EBC and the local distributor so this step is postponed for the time beeing

Image

as for the rear... i am running the OEM rotors from the vectra A... no plans for rotor replacement... at least for the time being.

Image

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Re: Comprehending proportional valves

Postby wolfsreign » Tue Apr 28, 2009 8:40 pm

hmmm okay then. thats time and money saved right there. haha. so then, basically ur brakes are like my car :) (front wise)
um.. also i dont think there are many "vectra A"'s in the junkyard here in the states, so do you know a cross reference? like the MK2/3, mofo said was a Pontiac over here.
i really want to get the rear's done. :)
thanks in advance
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Re: Comprehending proportional valves

Postby daewoomofo » Tue Apr 28, 2009 9:10 pm

hear you go wolfy
viewtopic.php?f=22&t=9564
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Re: Comprehending proportional valves

Postby MMamdouh » Thu Apr 30, 2009 10:00 am

found something about P valves:

p valves.JPG
(45.03 KiB) Downloaded 940 times


it seems the 3/40 will send more pressure to rear and the bias is based on how strong the front brakes are

this means the 3/30 are the ones to use when upgrading from 1.5 spec front brakes to 1.6 spec. front brakes

MMamdouh
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Re: Comprehending proportional valves

Postby wolfsreign » Fri May 01, 2009 7:59 am

+1
~wolf
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Re: Comprehending proportional valves

Postby zurcher1 » Thu Sep 29, 2011 8:45 pm

Anyone know where to get them in the USA? thats: 0.3/40 valve for nubie wagon..am changing from abs to standard brakes and using non abs master cylinder..
perhaps get the after market adjustable ones ??? which brand any good and also..where get in usa.

have rabbits and air cooled vw bugs and never even dreamed of abs....pain in rear to bleed and maintain...now getting old and not worth fixing?
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