Water coming out off PRV

[gazza]

Saggy car suspension, be it coil, Leaf or torsion springs are all the proof you need that springs do weaken over time.

[John V]

springs get tired...........my slinky always gets tired and stops when it gets to the bottom of the stairs !!!!!

[bizzard]

Saggy car suspension, be it coil, Leaf or torsion springs are all the proof you need that springs do weaken over time.

To be honest I can't remember suspension torsion bars ever weakening ie Morris Minor, old early 1950's MO Morris Oxfords, certain Mitsubishi's, E type Jaguar ect, though they are-were adjustable for ride height.

[MtB]

Saggy car suspension, be it coil, Leaf or torsion springs are all the proof you need that springs do weaken over time.

 

 

Leaf springs bend from overloading. Never seen a coil spring shorter than it's supposed to be!

[John V]

You've not owned a VW 412LE.....I can tell........first they get a little lower then they go bang, snap in the middle, each half then winds its way into the other and your front numberplate hits the road

[MtB]

As one-time owner of a 205GTi I'm familiar with broken coil springs, but that's not what we are discussing.

 

I still hold that springs do not simply 'weaken' in the original context, i.e. their deflection increases for a given load as time passes.

[gazza]

To be honest I can't remember suspension torsion bars ever weakening ie Morris Minor, old early 1950's MO Morris Oxfords, certain Mitsubishi's, E type Jaguar ect, though they are-were adjustable for ride height.

Old 205's start getting a bit saggy with time.

[John V]

I do not have enough evidence or experience to support the "weakening" side of the argument from a technical side but I do remember having to change valve springs on motorcycle engines when their length did not conform to manufacturers spec.

[gazza]

 

 

Leaf springs bend from overloading. Never seen a coil spring shorter than it's supposed to be!

it gets weaker resulting in lower ground clearance.

 

I guess your not familiar with shell boilers or steam generators - the prvs need testing every year to ensure they operate at the correct pressure, they can and do go out of calibration and need resetting. If your theory held water they would never need touching.

Edited May 30, 2015 by gazza

[MtB]

Old 205's start getting a bit saggy with time.

 

At which point if you examine them, they are always snapped. Or mine were anyway. I gave up buying Peugeot springs and used third party lowered and uprated springs. No more problems.

 

 

it gets weaker resulting in lower ground clearance.

 

I guess your not familiar with shell boilers or steam generators - the prvs need testing every year to ensure they operate at the correct pressure, they can and do go out of calibration and need resetting. If your theory held water they would never need touching.

 

The main reason steam PRVs need annual testing is in case their opening pressure has risen, surely!

 

But no, i have no experience of steam boilers.

[bizzard]

Old 205's start getting a bit saggy with time.

Never noticed it with them, probably because I was weakening with age at the same time.

[gazza]

 

At which point if you examine them, they are always snapped. Or mine were anyway. I gave up buying Peugeot springs and used third party lowered and uprated springs. No more problems.

 

 

 

The main reason steam PRVs need annual testing is in case their opening pressure has risen, surely!

 

But no, i have no experience of steam boilers.

So how would a spring become stronger if its properties don't change.....

 

The test is also to check the seat is in good condition and not pitted - usually done with a borescope

Never noticed it with them, probably because I was weakening with age at the same time.

My little 1989 1.1gl was getting lower with age. The new owner has helped it on its way somewhat, will try to find a picture if a pretty good Q car when I am back at work..

[bizzard]

I do not have enough evidence or experience to support the "weakening" side of the argument from a technical side but I do remember having to change valve springs on motorcycle engines when their length did not conform to manufacturers spec.

Due to the springs gradually over time getting annealed and softened by engine heat.

[John V]

Due to the springs gradually over time getting annealed and softened by engine heat.

 

Thanks for the explanation Bizz.........John

[gazza]

Due to the springs gradually over time getting annealed and softened by engine heat.

The springs will never get to the temperature required to start changing its properties, combustion chamber temps are very high but 2nd law of thermodynamics says the hotter to colder will always be so heat is soon dispersed add to that the cooling effect of the oil and air in the rocker cover and the temps soon fall way lower than that needed to achieve a change in the properties of the spring.

 

The valves on the other hand have a tough old time, Vauxhall took the unusual route of filling the valve stem with sodium on the old astra GTE engine to help.

[bizzard]

The springs will never get to the temperature required to start changing its properties, combustion chamber temps are very high but 2nd law of thermodynamics says the hotter to colder will always be so heat is soon dispersed add to that the cooling effect of the oil and air in the rocker cover and the temps soon fall way lower than that needed to achieve a change in the properties of the spring.

 

The valves on the other hand have a tough old time, Vauxhall took the unusual route of filling the valve stem with sodium on the old astra GTE engine to help.

They certainly can seem to shorten over a long period of heating as can oil pressure relief valve springs.

[gazza]

I always understood the shortening to be due to constantly being worked.

 

Cylinder head temps of 550°c + would be a big worry, especially on a liquid cooled engine!

[bizzard]

I always understood the shortening to be due to constantly being worked.

 

Cylinder head temps of 550°c + would be a big worry, especially on a liquid cooled engine!

Probably the expansion and retraction coupled with continually being worked of the metal during continual heating and cooling gradually altering the molecules, Though oil pressure relief valve springs or indeed the calorifier PRV springs are only quite gently worked compared to the fast hammering of engine valve springs.

[gazza]

Probably the expansion and retraction coupled with continually being worked of the metal during continual heating and cooling gradually altering the molecules, Though oil pressure relief valve springs or indeed the calorifier PRV springs are only quite gently worked compared to the fast hammering of engine valve springs.

Yup,

 

Which led ducati amongst others to go for mechanical operated valves, culminating with the pneumatic valves in F1 engines - all done to get round the dreaded valve bounce at high RPMS

[bizzard]

Yup,

 

Which led ducati amongst others to go for mechanical operated valves, culminating with the pneumatic valves in F1 engines - all done to get round the dreaded valve bounce at high RPMS

My first car, a 'Rosemary' a 1936 Ford 8 Y type would bounce valves at about 3,500 RPM, hold all the valves open and the engine would cut out and chime back in when the revs dropped, I regularly did this in second gear. Most old S/V engines had soft-weak valve springs especially the old S/V Ford engines including the 1172cc E93A and 100E's all had very soft valves springs, probably on purpose to act as governors to prevent over revving.

[Neil Smith]

My first car, a 'Rosemary' a 1936 Ford 8 Y type would bounce valves at about 3,500 RPM, hold all the valves open and the engine would cut out and chime back in when the revs dropped, I regularly did this in second gear. Most old S/V engines had soft-weak valve springs especially the old S/V Ford engines including the 1172cc E93A and 100E's all had very soft valves springs, probably on purpose to act as governors to prevent over revving.

What no electronic rev limiter on old rose how did she cope.

 

Neil.

[bizzard]

What no electronic rev limiter on old rose how did she cope.

 

Neil.

Well, the nearest they got to an electronic rev limiter was in the 1960's, a rotor arm with spring loaded HT centrifugal contact which retracted at a certain revs and cut the ignition spark to the plugs, Jaguar E type, Mk11 3,4, 3.8, 4.2 S types, plus others, I recall to mind.

Edited May 30, 2015 by bizzard

[Alan Saunders]

Let's take a simple case, the so called, misnamed 'spring balance', you probably have one in your bathroom and/or kitchen. Even with daily use, less than the constantly varying pressure on a PRV, the modulus of elasticity remains more or less constant but the length varies with ambient temperature as well as the repeated compression/expansion.

 

A 'spring balance' invariably has a means of setting it to zero whereas the typical PRV does not. The spring-rate may not change significantly but the 'zero-point' will.

 

Alan

[blackrose]

I was passing Screwfix today so dropped in to see if I could buy a new PRV assuming it was something they would have.

 

All I could find was pressure reducing valves.

 

But it did get me thinking... Could I use one of these after my accumulator to even out the pressure or would it lead to other problems?

 

http://www.screwfix.com/p/honeywell-pressure-reducing-valve-with-gauge-15mm/69396?_requestid=235768

[Phil Ambrose]

I have used one of these on a previous boat and it seemed to work OK, I'm guessing in your application anything downstream of the PRedV would be at whatever pressure you set it at.

Phil