Grommet vs Connector In Power Brake Booster Design

(Though i have a degree in mechanical engineering since 1986 from Romania, it is in Machine Tools and not Automotive Engineering. After i graduated, most of the work i've done was in computer programming though at the beginning related to engineering CAD after which i swicthed to accounting, payroll and medical insurance. Also my level of English when i came in the United States, especially in the technical area was much lower than today, after i started writing on social media. Thus it is only recently when i understood the below described phenomena and also became capable of describe it.)

A rubber grommet is a ring with a groove on the outside that fits in a hole and helps with the passage of a pipe, cable or connector through that hole, preventing the last one touching the edges of the hole. Most common use of grommets, as described in this Wikipedia picture, is for passing cables through holes.

In automotive industry they are also used for passing and sealing of ribbed connectors and holes, mostly in PCV valve or power booster applications. Here is the image of a power booster check valve with two connectors on each side (in and out). It is a one way valve with a spring and seal inside that allows the flow of air in one direction only and it ends with two ribbed connectors, of which one goes into the power booster grommet and the other to the power booster vacuum hose that at the other end is connected to engine manifold or throttle body on the manifold side. The function of this valve is to make sure that vacuum does not escape from the booster or air it's not getting in immediately after the engine stops, ensuring one or two brake cycle in case of engine failure or sudden stop while the vehicle is driven. For the purpose of this discussion it does nothing more than an L shape connector.

A brake power booster is a big cylinder with one or two diaphragms inside that helps with braking by adding extra force to the master cylinder when a smaller brake force is applied on the pedal. The extra force is generated by the suction power of the engine on the admission cycle, which in automotive terms is named manifold vacuum, or the difference of pressure between the inside of the manifold and atmospheric pressure applied on the opposite sides of the diaphragm.

Many don't understand. In combustion engines the air volume necessary for running the engine is small, at least at idle and under no load conditions. Thus, the flow of the air in the engine is restricted by a round shape valve called throttle that turns inside a cylindrical air passage with the same diameter with the throttle called throttle body with the pressing of the "gas" pedal. At idle the throttle is in perpendicular position with the air flow and closing the passage. A small amount of air (by)passes usually through a parallel passage that is also controlled by the computer through a solenoid or actuator, that is open only at idle. On the rotation axis of the throttle there is a potentiometer like sensor (similar with those in older audio devices) that turns with the throttle, thus transmitting to the computer a variable voltage that tells the computer how much the throttle is opened. Because of this severe restriction of the air flow inside the engine, vacuum is created on the intake side of the throttle. This vacuum is available and engineers long time ago figured they could use it for powering different devices and actuators in the vehicle as if would come from a vacuum pump), as the brake power booster.

In a normally running engine, at idle, this vacuum generates a difference of pressure with the atmospheric pressure of or above 22 inches mercury, that is about 11 psi and can go a little higher but obviously not higher than the atmospheric pressure itself that is about 14.7 psi since the difference it's generated by vacuum, or suction, or lack or pressure that can obviously cannot go lower than zero. 11 psi is equivalent with about one third to almost half of the pressure inside a tire that is above 32 psi.|

Here is a picture with a power booster that uses a grommet for passing the connector of a check valve.

Another type of design for solving applying manifold vacuum to the power booster described in the picture below uses instead of a grommet a connector that is part or welded or pressed on the power booster in the same place where the grommet hole is in the grommet solution, connector that is similar to the connector used on the other end of the hose as in both solutions, in which case the check valve is placed somewhere else like inside the booster.

Due to the way it is created, by the reciprocating motion of the pistons inside the cylinders that follows a time dependent sine pattern, engine vacuum has a pulsating nature that is partially smoothened by the volume of (low pressure) air inside the manifold and hoses (there are other pneumatic devices that are also fed with the pressure difference of pressure between inside the manifold and surrounding air that are connected to the manifold side of the throttle body though smaller and less important that also hold a certain volume of the same low pressure air in all the hoses and devices).

In a normally running engine, at idle, vacuum is  about 22 inches, relative or lower than atmospheric pressure. When the gas pedal is slightly pressed and throttle opens a little, around 2000 rpm, the vacuum gets even higher, closer to zero pressure or absolute vacuum or 14.7 psi relative to atmospheric pressure due to increasing need of engine for air because of faster movement of the pistons and the throttle's opening resistance. When the throttle is opened even more, thus allowing more air freely into the manifold the vacuum starts to decrease again.

The more vacuum in the manifold, the more pulsating is the pressure difference due to increasing amplitude of the sine wave due to reciprocating motion of the pistons.

Also. Due to various dynamic forces the engine has a tendency of moving or vibrating on its rubber mounts, mostly following the cycle of pistons' reciprocating movement, but also the rpm. There are certain rpms that make the engine move more or at higher amplitudes than others due to resonance phenomena.

Also, all the hoses, including power booster vacuum hose are not rigid and move around together with the engine having their own moving pattern and resonance with certain rpms.

The grommet in the grommet solution in all different design variations (i've seen so far) have the length and diameter of the groove comparable with the sheet metal and the hole they seal, design that cannot generate a sealing force on the wall of the booster. Thus the sealing is being insured by the difference of pressure between inside and outside of the booster applied on the outer side of the grommet that presses against the booster's wall.

The check valve's connector on the grommet side has a slightly bigger diameter than the hole of the grommet and it is ribbed, and when is inserted into the grommet it causes very hard to predict deformations of both parts which in this case are static but asymmetrical due to the weight of the hose but at least at the beginning of its life and at idle it seals the vacuum or at least partially, up to a certain pressure difference or pulsating amplitude at certain rpms.

Thus there are two sealing surfaces regarding the grommet. One is between outer rim of the groove and the sheet metal around the hole and one is between the hole and the connector.

As i said the vacuum hose has its own weight. This weight is applied on the grommet side as well but with dynamic variations following the different relative motions between the grommet and the hose, generating variable forces that are impossible or very hard to predict that are in the end applied onto and sustained by the grommet, causing it to slightly change shape many times a second, or causing dynamic deformations, following the relative motion of the engine and the hose. Those changes of shape are asymmetrical due to direction of the variable force being applied on the grommet and very hard or impossible to predict, in the end changing the sealing surface, in a dynamic way and increasing it on one side and decreasing on the other.

In conclusion, both the pulsating nature of the engine manifold vacuum and the forces generated by the hose moved by the engine moving on the mounts deform the grommet dynamically, combined can change the sealing areas and pressures on the sealing surfaces of the grommet, possibly leading to small, pulsating leaks that might appear only on certain rpms and engine loads.

The power boosters are oftenly painted on the outside to check corrosion. The sealing surface between the grommet and the power booster is also painted. Paint thickness can be irregular causing unpredictable variations on the final shape and smoothness of the sealing surface and can also degrade in time or even be peeled or chipped due to age causing irregularities to grow in time and sealing to decrease, thus increasing  the pulsating vacuum leak.

Peeled, eroded paint an a small indentation at the power booster grommet hole

The grommet solution compared to welded connector solution brings several more areas than need to be sealed in the vacuum transmission assembly between throttle body and booster, that is throttle body connector-hose, hose-check valve, check valve-grommet and grommet-power booster.

Grommets are made of rubber. Rubber is a material that often has irregularities but also changes properties in time due to aging. Constant pressure like from the ribs of the connector can cause grooves inside the hole of the grommet thus in time decreasing sealing capacity on that side. Also rubber looses elasticity with age thus the initial installation pressure and sealing capacity between grommet and check valve connector and capacity of following the irregularities on the painted area.

The welded connector design is much simpler, and cost comparable solution, it follows the solution on the other side of the hose, has less sealing surfaces and much less like to cause vacuum leaks.

Uncontrollable vacuum leaks in the end translates by air flowing in the engine in uncontrollable ways, bypassing the throttle body and throttle.

Small intermittent vacuum leaks on carburrated engine can cause trouble by changing in unpredictable ways the fuel/air ratio.  The computer responds promptly by the reading of the oxygen sensors, thus adding more fuel.

But on injected engines even small vacuum leaks are critical because in injected engines fuel/air mixture is adjusted by a computer based on reading from one or more oxygen sensor inside the exhaust system, among others. The more oxygen the sensors read due to a vacuum leak or air escaping uncontrollably into the manifold, the more fuel it adds. Also air/fuel ratio is adjusted by the computer using readings from other sensors, including throttle positioning sensor and pressure sensors inside the manifold and intake hose. Air flowing into the manifold due to unpredictable, intermittent leaks translates into reading in the sensors than cause the engine running erratically and mainly increasing fuel consumption with all its consequences, like more fuel burning with the extra air inside the exhaust and catalytic converter, shortening the life of the catalytic converter and overheating other components of the vehicle, like floor, transmission and clutch. Extra fuel consumption also translates in more fuel being used, extra cost, pollution, etc.

The following pictures are done with my old check valve and hose and a new original grommet.

All the deformations that remain permanent due to aging of the grommet, abrasion of the paint, inevitably lead in time to more important vacuum leaks that can lead to decreasing braking capacity, but that is not obvious since it occurs very gradually and the driver gets used to. Though vacuum is present in the booster, it is diminished due to vacuum leaks that appear only in this design up to a point when the computer finally sets an error that usually indicates a lean condition (too much air in the air/fuel mixture), because through its oxygen sensors it actually measure the amount of oxygen left after the burning cycle inside the cylinder that is increased in case of vacuum leaks or more air bypassing the throttle thus unaccounted for by the TPS sensor inside the intake manifold. But when usually that happens that engine has been functioning abnormally for too long and other components have been damaged by overheating. Also the vacuum leaks even at the beginning of the life of this vehicle that are due to the grommet solution are intermittent, and the computer is programmed to put a check engine light only after a contentious malfunctioning or a high reading on one of the oxygen sensors of a certain period of time, cycles and events, that only happens when the vacuum leak grows bigger and/or gets permanent.

All these consequences can be averted if the pressed or welded connector solution is used instead of the grommet one.

It is hard for me to estimate the amount of fuel being used by multiplying this type of failure due to a faulty design to the the number of vehicles that still use it, but i estimate it in the enormous area.

Cars and Stuff

Mc

Question. Do they know?

Direcția Apelor Bacău

Revizuit, 20/01 2016

A fost o inundație mare în județul Bacău parcă în orice caz într-o localitate unde era un baraj care aparținea de Direcția Apelor Bacău, mi se pare deja Regia Autonomă Apele Române. Berești Tazlău în 28-29 iulie 1991. (Bere= bear, Taz = Austraian Devil whatever).

Eu am lucrat la ELBAC până în vara aceea ca programator la oficiul de calcul. Șefa mea era o tipă Nuți care semăna cu Madonna. Mai era o tipă Nela care semăna cu Frida de la ABBA și un tip care semăna cu Boy George. A și Pușcuță, un tip care dacă n-ar fi fost brunet cu ochi negri aș zice că semăna cu Sean Penn. Erau mai mulți care semănau cu mai mulți dar n-are rost să-i numesc pe toți. Unul Liviu cu mustață proaspăt venit la oficiul de calcul. Care după aceea a fost la un curs și a ajuns să mă învețe el pe mine trucuri din FoxPro (un limbaj de PC devreme).

La început la ELBAC lucram în turboPascal pe niște calc Z80 cu floppy. Apoi directorul a pus niște bani și am adus eu de la Fabrica de Calculatoare București un PDP compatibil (Era un inginer pe acolo Puiu Mandler care chiar semăna puțin cu Seinfeld care tot mă trimitea la Samsung la București, dar nu aveam ce face cu un PC, PDP-ul avea 16 terminale pentru culegere date). Pe acela m-am apucat să fac un nou program de salarii. Instigat de Pușcuță, cât era Nuți (șefa) în concediu.

În timp ce ea era în concediu, Pușcuță a organizat un complot să-i ia locul lui Nuți din care parte centrală era noul program de salarii pe care trebuia să-l termin. Când a venit Nuți din concediu eu nu terminasem programul decât partea de avans, eram epuizat de enorm de multe ore suplimentare, Pușcuță și-a dat demisia și eu după el (de onoare adică).

Și am prins un contract la R.A.Apele Române printr-un amic care a devenit mai recent dușman. Am lucrat acolo vreo 6 luni și am terminat programul.

Dar am văzut recent la BBC un interviu cu Don McLean și mi se pare că seamănă cu directorul economic de atunci, Angheluță. Mai era la oficiu la Direcția Apelor o tipă mișto tare care mi se pare că seamănă cu Penelope Cruz. (A trecut un Harely chiar când scriam numele acestea). Și una care semăna cu "Laura Stoica".

Într-o seara am primit o ofertă de la o firmă în care era băgat Angheluță să le fac un program până dimineață (peste ce lucram eu acolo la salarii). Plăteau bine, cred un salariu pe o lună pe atunci pentru o noapte de scris și testat un program. Angheluță (cel care semăna cu Don McLean, deja în vârstă pe atunci, adică dacă acum are 70 de ani atunci avea 48) a aranjat să pot sta la calc. (mini, PDP) în noaptea aceea cu tipa care semăna cu Penelope (era operatoare). Man ce mișto era fără machiaj nimic. Dar cam supărată tot timpul și vorbea câte un cuvânt două. Spunea că taică-su era prof de mate și a bătut-o cu capul de masă fiindcă era cam proastă. Dar acum cred că pur și simplu nu știa română.

Nu știu dacă inundația a fost înainte, după sau chiar în acea noapte. Nu am făcut niciodată legătura până acum.

Spre dimineață am condus-o pe "Irina" undeva la un bloc în Miorița cred. Stătea supărată și serioasă în fața mea și nu zicea nimic. Nu am zis nici eu nimic, adică am zis noapte bună sau bună dimineața și ea a plecat. După aceea m-am dus la Contexpert unde era șef unul Doru Corban și le-am predat programul și print-out-ul. Era un tabel, o progresie de calculat impozit pe salarii. Dar nu a ținut mult. Pe atunci legile se schimbau mereu.

La vreo săptămână două a venit tipa cealaltă care semăna cu Laura Stoica, secretara directorului și m-a invitat la un weekend în patru împreună cu un tip de pe la oficiu.

La un moment dat (după inundație) o tipă blondă de la oficiu mi-a zis că danezii oferă azil politic la toți cei din zona sinistrată. Cred că ea a și plecat. Dacă era ea. Nu știu sigur dar poate tipa era însărcinată.

Bine au fost multe faze pe acolo nu pot să le povestesc pe toate. Șeful birou salarii Adam cu care lucram non stop semăna cu CTP. Azi când mă gândesc, pare logic că programul acela al meu s-a desfășurat paralel cu tot ce făceau ei la oficiu. Poate că acel calc la care lucram eu nu a funcționat vreodată pe bune... Și miile de modificări pe care mi le cerea mereu Adam... Nici nu vreau să mă gândesc. Eu aveam terminalul într-o cameră undeva la mansardă și mai era unul în birou la salarii unde lucram cu o tipă care semăna cu Rodica Mandache.

Nu știu exact câți și cine au plecat în Danemarca.

Din câte știu eu, barajul putea fi salvat dacă era deschis. A plouat enorm, în 24 de ore cât în câteva luni. Poarta sau cum se cheamă a barajului era acționată electric și manual, a picat curentul iar tipul care trebuia s-o deschidă nu a mai ajuns la timp. Apa a curs pe lângă și a spălat un dig.

Pentru câteva ore a fost un debit egal cu al Dunării pe acolo. Dar astăzi încep să mă îndoiesc, ca de orice catastrofă care se petrece în zone îndepărtate, greu de verificat de public.

Și la un moment dat Adam a vrut să mă angajeze, dar nu la oficiu, fiindcă "nu avea loc pe schemă de toate putorile directorului de acolo ci într-un birou de ingineri".

În România puțini știu melodia asta dar în America e una din cele mai celebre.



http://www.bibliaortodoxa.ro/carte.php?id=4&cap=12

Rhododendron, Oregon

Never knew. Never cared. Today i paid more attention to this https://en.wikipedia.org/wiki/Rhododendron#Toxicology

Here in Portland there are maybe 1 plant for 10 people. "It is the national flower of Nepal."

Hm. Surrounded by coincidences. Today i realized that in every place i lived i had one next to door and/or window. Don't know if it's toxic only by smelling it. Probably in combination with something else, like some building materials, cigarette smoke or exhaust. Maybe just as cover, the main amount coming from somewhere else.


Here is 1122 SW Stephenson, my first address in Portland where i was living at Mladin's house. Here i met Mladin's daughter, a girl that looked like Malin from Ace of Base. I was living in a small room at ground level next to the furnace, under the balcony. 4 months at this address September-December 1995.


At Fox Pointe in Vancouver, 3015 NE 57th as remember from documents. But i don't believe i've been staying next to the laundry room... Anyways, the only rhododendron i could see here was in front of 3017, on the right in the picture. But it's also been 20 years since... The apartment seems very small but actually was bigger than the one i live in right now.


6810 SW Hall Blvd @16, Beaverton. Sussex Village. 14 years at this address. The upper right window is the kitchen. The same 600 sqft living space as before in Vancouver and after in Lake Oswego.






47 Eagle Crest Lake Oswego. Balcony in the upper middle-right of the picture. 2nd level. Here since February 2010.


I've been there the other day and moved the rock (fresh ground upper right corner). There it was smelling like in a restaurant with don't know a dozen people smelling simultaneously additive free cigarettes).