Polyair with a differance, opinions please

[joel0407]

I've been doing some searching but haven't found any information about this.

Polyair or the like are USUALLY used to level a vehicle that has standard rated spring and carrying extra load, wether it be from a trailer or load in the vehicle.

I have recently purchased a Discovery 2 which has the SLS air bags removed and fitted with coils. Obviously the coils whilst fine when unloaded it was not enough spring for load carrying so in coil air bags were fitted (polyair).

So why only use the airbag when the coil spring cant help. Apparently these air bags can be inflated upto 100psi but from a little research 25psi seems to be plenty for the heaviest loads and they need to be kept at around 5 - 7psi when not required to keep the bags from being pinched or damaged in other ways.

I have red how good the SLS air is but also a little temperamental. If a valve fails, the compressor fail or a bag gets punctured you can be stranded with the suspension sitting on the bump stops.

I intend to purchase some standard height springs but with a spring rate far less than is required to just hold the vehicle level. Then I will connect the SLS system to the in coil air bags (polyair) and allow the SLS system to level the vehicle. I cant see why this has not been done before or maybe it has and the person just hasn't shared the experience.

I will appreciate your thoughts.

Happy Days.

[BigJon]

That isn't how polyair and similar bags work.

They are designed to be inflated before the load is applied to the vehicle (before the suspension sags). They then expand between the coils artificially increasing the spring rate.

They are not designed to lift the vehicle once the load has been applied.

[joel0407]

That isn't how polyair and similar bags work.

They are designed to be inflated before the load is applied to the vehicle (before the suspension sags). They then expand between the coils artificially increasing the spring rate.

They are not designed to lift the vehicle once the load has been applied.

Can you explain some more please?

Does it matter if the bag is inflated before or after the load is applied. The effect is the same that the vehicle is leveled.

ie. If the vehicle is loaded and sags then air is applied to increase the spring rate the vehicle will return to the original height. Or not. If BigJohn can explain otherwise.

[twr7cx]

Just refit the SLS system back in place. Generally the failures are occurring in units that are 10 years old or more and are still on the original rubber components... I wouldn't use a drive belt or coolant belt for 10 years without replacing it, so why would rubber airbags be any different.

If someone was particularly worried about the air bags, they're pretty easy to replace so you could carry a spare and do it out bush and also fit a shrader valve to use a tyre inflator to reinflate it if the air compressor was to fail.

[twr7cx]

Can you explain some more please?

Does it matter if the bag is inflated before or after the load is applied. The effect is the same that the vehicle is leveled.

ie. If the vehicle is loaded and sags then air is applied to increase the spring rate the vehicle will return to the original height. Or not. If BigJohn can explain otherwise.

I would assume what happens is you inflate the poly bag prior to putting the load on.
Due to the inflation, the bag expands and bulges out through the gaps in the spring.
You now have the bulged air bag between the spring coils.
Put the load on, and the spring has resistance stopping it's ability to compress.
The resistance is the bulged part of the air bag between the spring coils.

http://www.polyair.com.au/

[joel0407]

I would assume what happens is you inflate the poly bag prior to putting the load on.
Due to the inflation, the bag expands and bulges out through the gaps in the spring.
You now have the bulged air bag between the spring coils.
Put the load on, and the spring has resistance stopping it's ability to compress.
The resistance is the bulged part of the air bag between the spring coils.

Polyair Springs air bag suspension lift kits (http://www.polyair.com.au/)

I haven't red this anywhere. I believe the increased rate comes from the air pressure. The spring mearly contains the bag.

Happy Days.

[joel0407]

Just refit the SLS system back in place. Generally the failures are occurring in units that are 10 years old or more and are still on the original rubber components... I wouldn't use a drive belt or coolant belt for 10 years without replacing it, so why would rubber airbags be any different.

If someone was particularly worried about the air bags, they're pretty easy to replace so you could carry a spare and do it out bush and also fit a shrader valve to use a tyre inflator to reinflate it if the air compressor was to fail.

I considered it but I would need to replace the whole system. I have red that any of the components can fail. I know I could carry a few small parts to limp it home like being able to isolate the bags should a valve or the compressor fail and spare bags should one of them fail.

The thing is I already have the the polyair bags there and I could get this working for less than the cost of 1 LR bag.

Happy Days.

[simonmelb]

I considered it but I would need to replace the whole system. I have red that any of the components can fail. I know I could carry a few small parts to limp it home like being able to isolate the bags should a valve or the compressor fail and spare bags should one of them fail.

The thing is I already have the the polyair bags there and I could get this working for less than the cost of 1 LR bag.

Happy Days.

With the A$ at it's highest against the GBP in 28 Years it's a good time to buy stuff from the UK. Replacing all wear parts would cost you GBP 271 for the complete compressor/valve assembly and GBP 58 each for the air springs.

Over 10 years service life that's not a lot per year.

Having done a 9 month around OZ trip with SLS I would save up your $ and put back the SLS the way LR designed it, as it works really well.

If you're worried you could take your whole old spare compressor/valve assembly and an air spring!

Cheers
Simon

[joel0407]

I plan to weight the rear of the vehicle empty and then add an estimated light load (enough for a days outing).

I'll measure the travel from standard height to the bump stop and length or the standard springs.

I'll then use these measurments to calculate the required spring rate for the vehicle to sit and inch or so of the bump stop with the standard spring. Should anything go wrong with the air system, that travel should be plenty to just get me home.

Then I will connect the in coil air bags to the SLS system and allow it to inflate the bags, increasing the spring rate and restoring vehicle height.

The load of my unlaidened vehicle will then be shared between the coil spring and the air bag (air spring). If the load is increased from a trailer or cargo, the SLS system will increase the pressure and effectivly increase spring rate and maintain the vehicle ride height.

The only differance I can see is usually an unlaidened vehicle relies soly on the coil spring and when load is applied, air is added and the load is then shared between the coil spring and the air bag. My unlaidened vehicle will already have the load shared.

Happy Days.

[joel0407]

With the A$ at it's highest against the GBP in 28 Years it's a good time to buy stuff from the UK. Replacing all wear parts would cost you GBP 271 for the complete compressor/valve assembly and GBP 58 each for the air springs.

Over 10 years service life that's not a lot per year.

Having done a 9 month around OZ trip with SLS I would save up your $ and put back the SLS the way LR designed it, as it works really well.

If you're worried you could take your whole old spare compressor/valve assembly and an air spring!

Cheers
Simon

That's not bad at all. I thought they where $350 odd per bag.

Happy Days.

[joel0407]

With the A$ at it's highest against the GBP in 28 Years it's a good time to buy stuff from the UK. Replacing all wear parts would cost you GBP 271 for the complete compressor/valve assembly and GBP 58 each for the air springs.

Over 10 years service life that's not a lot per year.

Having done a 9 month around OZ trip with SLS I would save up your $ and put back the SLS the way LR designed it, as it works really well.

If you're worried you could take your whole old spare compressor/valve assembly and an air spring!

Cheers
Simon

Actually that adds up prety quickly 271 + 58x2 = GBP 387 (About AUD$545).

I recon a couple spring wont cost me $200.

[vnx205]

I would assume what happens is you inflate the poly bag prior to putting the load on.
Due to the inflation, the bag expands and bulges out through the gaps in the spring.
You now have the bulged air bag between the spring coils.
Put the load on, and the spring has resistance stopping it's ability to compress.
The resistance is the bulged part of the air bag between the spring coils.

Polyair Springs air bag suspension lift kits (http://www.polyair.com.au/)


I haven't red this anywhere. I believe the increased rate comes from the air pressure. The spring mearly contains the bag.

Happy Days.

It isn't that simple.

Polyair specifically says not to use the air bags to lift the vehicle.

GENERAL MAINTENANCE TIPS: After fitting kits and/or extension leads, inflate air bags to 175 KPA / 25 lbs and test for air leaks by applying a liquid soapy solution to all valve cores, fittings and connections.


Caution - Do not inflate air springs while vehicle is on frame hoist. Vehicle must be standing on its wheels before bags are inflated.


Maintain at least 35 KPA / 5 PSI of air pressure in the Air Lift Bags to prevent chaffing.
Inflate your Air Bags before loading your vehicle to maximum pressure indicated on fitting instructions.
Do not attempt to raise a loaded vehicle by inflating Air Bags. If loaded, jack up body until level, then inflate.
It is recommended that tyre pressure be increased by 14 KPA (2 lbs) above normal for each 45 kg / 100 lbs total overload on the axle.
POLYAIR SPRINGS recommends that the kits be used to support loads which are within the vehicle manufacturer's rated GVW
(My emphasis)

Polyair Springs - Airbag World | Air Bag Suspension Specialists (http://www.airbagworld.com.au/polyair-springs-airbag-suspension.html)

It isn't just the pressure that helps carry the load.

[strangy]

As the numerous and relevant SLS threads have apparently been read and given what others have already said. And you still think this path may be an option
My opinion..... Don't waste your time and money on this.

Cheers

[DeanoH]

I reckon you're 'over thinking the problem', if indeed there is one.

Does the vehicle sit well, is the rear sagging with normal load/use and with say 5 psi in the polyairs ? If so all OK so far. :)

With the vehicle loaded and 25 psi in the poly airs does the vehicle still sit and drive OK ? If so you haven't got a problem so why all the worry ? :confused:

Don't even think about 100 psi in your polyairs :eek:, you are correct that 25 psi is tops.

Another benefit with your polyairs is that as load increases and the springs compress, say when driving over rough ground, the polyairs become harder to compress with load giving a 'variable rate' effect. This means you don't bottom out and the strain/load on the vehicle its occupants and suspension is minimised.:D

Do you have std. springs ? It is important to have the correct length of polyair for the springs fitted. There should be little or no space above/below the airbag with the vehicle unloaded, a plastic spacer is often installed under the airbag to achieve this.

I've had polyairs on the RRC for 15 years now and on the D2a for about 8 years and have towed caravans and a camping trailer for many miles around Oz with no problems. The boys now use the RRC for bush driving and pump up the polyairs for a bit more lift and stiffness in the rear.

With quality heavy duty shockers I reckon you could be good to go with what you've got. :)

Deano :)

[joel0407]

It isn't that simple.

Polyair specifically says not to use the air bags to lift the vehicle.


Inflate your Air Bags before loading your vehicle to maximum pressure indicated on fitting instructions.
Do not attempt to raise a loaded vehicle by inflating Air Bags. If loaded, jack up body until level, then inflate.
It isn't just the pressure that helps carry the load.

Ok. Now I am being convinced to restore the SLS with LR air bags.

Thanks for the link. Id been getting most of my info from here Polyair Springs air bag suspension lift kits (http://www.polyair.com.au/) and it's limited what info there is here.

What I'm getting from this is it is a bad thing to be changing the pressure in the polyairs

[joel0407]

I reckon you're 'over thinking the problem', if indeed there is one.

Does the vehicle sit well, is the rear sagging with normal load/use and with say 5 psi in the polyairs ? If so all OK so far. :)

With the vehicle loaded and 25 psi in the poly airs does the vehicle still sit and drive OK ? If so you haven't got a problem so why all the worry ? :confused:

Don't even think about 100 psi in your polyairs :eek:, you are correct that 25 psi is tops.

Another benefit with your polyairs is that as load increases and the springs compress, say when driving over rough ground, the polyairs become harder to compress with load giving a 'variable rate' effect. This means you don't bottom out and the strain/load on the vehicle its occupants and suspension is minimised.:D

Do you have std. springs ? It is important to have the correct length of polyair for the springs fitted. There should be little or no space above/below the airbag with the vehicle unloaded, a plastic spacer is often installed under the airbag to achieve this.

With quality heavy duty shockers I reckon you could be good to go with what you've got. :)

Deano :)

Yeah, I think the current coils and polyairs are all set up correctly. I only bought the vehicle last week.

The main reason for playing around with this stuff is to improve it. I currently dont have any intention of towing anything or carrying anything too heavy so as it is I have no use for the polyairs.

All the original SLS stuff is there and to hook it up to the polyairs would only take a little bit of plumbing. I dont know if it's still in working order or whats wrong with it.

The vehicle will be on a transporter to Darwin tomorrow and then I'll be there with no tool until I find a home to rent and get moved in.

The SLS valves seem to be clicking in an attempt to get the vehicle to where it wants it, not where it is. This apparently (from previous owner) flatens the battery. I have since learned I can disable this with Nanocom. The fuse is already pulled and it still clicks. Either the springs dont allow it to go low enought for the SLS or I dont have the polyair pumped up high enough.

My options were

1. Leave it as it is with the SLS stuff and polyairs being wasted. (Free)
2. Restore the original SLS. (Expensive)
3. Combine the 2 and get the best of both. (Cheap for a couple of coils)

1. Boring.
2. Best option but not going to happen too soon due to cost
3. Now starting to seem as it wont work.

Happy days.

[BigJon]

What I'm getting from this is it is a bad thing to be changing the pressure in the polyairs

No, changing pressures in the polyairs is perfectly normal. I do it, in fact I did it on the weekend. What you mustn't do is inflate the polyairs to try to lift the vehicle back up after the load is applied.

I had a trailer with a small tractor behind my RRC on the weekend. Once I had loaded it I looked at how much the vehicle had sagged. Then I put a trolley jack under the rear crossmember and jacked it back up to the correct ride height. Then I increased the pressure in the airbags.

As an alternative I could have increased the airbag pressure prior to hooking the trailer up, but I forgot :eek:.

[joel0407]

No, changing pressures in the polyairs is perfectly normal. I do it, in fact I did it on the weekend. What you mustn't do is inflate the polyairs to try to lift the vehicle back up after the load is applied.

I had a trailer with a small tractor behind my RRC on the weekend. Once I had loaded it I looked at how much the vehicle had sagged. Then I put a trolley jack under the rear crossmember and jacked it back up to the correct ride height. Then I increased the pressure in the airbags.

As an alternative I could have increased the airbag pressure prior to hooking the trailer up, but I forgot :eek:.

Yes of course. Changing pressure is normal, I'm just confusing changing pressure with changing height.

Happy Days.

[joel0407]

I recieved a call from Polyair this afternoon as I had asked a question through the "Contact us" on their web page.

The answer was: Poly Air, in coil air bags cant be used to lift a vehcile because they grip the insides of the springs and cant expand up. He gave me an example of a person he had sold a set to, installed them and then measured the rear of his vehicle with the trailer on, inflated the poly air bags and found no change in height so requested a refund. Poly Air being the good guys they are refund the guy even though he wasn't following the instuctions.

Poly Air said that should have the guy driven up the road a little the bags would have moved with the spring movement and settled heigher. This all makes sense to me now.

Next problem he suggested is the SLS system can provide far more pressure then the Poly Air bags can handle and left to it's own devices it could just pop a bag. This also made sense as the SLS system would realise the vehicle is sitting too low with under rated springs and start providing pressure. Intead of the vehicle rising, it would simply push the bags out against the spring as stated above, then it would continue to apply pressure until the pressure was so high it pushed an end out of a bag and pop.

Anyway that idea is out the window now and it looks like once I'm settled in Darwin, I'll be restoring the LR SLS the way it was designed to be and maybe with a new set on shocks all the way around.

Happy Days.

Thanks for your help and ideas fellas.

[wardy1]

OMG! This thread has become sooo complicated!

1. The Original SLS should have been retained but it wasn't. Shame really, wish I had it.
2. You don't intend carrying excessive loads or towing anything particularly heavy. The Poly's will do a great job at 25psi if you're fully loaded and about 15psi if its a w/e away load up. this keeps a nice ride and good control of the rear suspension.
3. Poly's were never designed as a lifting tool.
4. If you run less than 5psi in them the bags will scrub out by rubbing on the movement of the the coils.

Really not sure why sometimes we get bogged down with lots of theory when there are manufacturers specs which set out the proper usage of a product. The pro's and con's of SLS notwithstanding. This member DOESN'T currently have SLS but DOES have a very good system in place to keep his vehicle pretty level (providing that the pressure is lifted to prior to the load)and articulate over most surfaces...... where's the problem?

[schuy1]

Too many blasted cooks methinks!!! :D

[ozscott]

I recieved a call from Polyair this afternoon as I had asked a question through the "Contact us" on their web page.

The answer was: Poly Air, in coil air bags cant be used to lift a vehcile because they grip the insides of the springs and cant expand up. He gave me an example of a person he had sold a set to, installed them and then measured the rear of his vehicle with the trailer on, inflated the poly air bags and found no change in height so requested a refund. Poly Air being the good guys they are refund the guy even though he wasn't following the instuctions.

Poly Air said that should have the guy driven up the road a little the bags would have moved with the spring movement and settled heigher. This all makes sense to me now.

Next problem he suggested is the SLS system can provide far more pressure then the Poly Air bags can handle and left to it's own devices it could just pop a bag. This also made sense as the SLS system would realise the vehicle is sitting too low with under rated springs and start providing pressure. Intead of the vehicle rising, it would simply push the bags out against the spring as stated above, then it would continue to apply pressure until the pressure was so high it pushed an end out of a bag and pop.

Anyway that idea is out the window now and it looks like once I'm settled in Darwin, I'll be restoring the LR SLS the way it was designed to be and maybe with a new set on shocks all the way around.

Happy Days.

Thanks for your help and ideas fellas.


My coil-rites can have 200kg from my boat on them, sag and then as I pump them up they lift the back end. I will have to stop that. ..done it for 3 years but will have to air up first. I know by now they like 20 pound. Actuality 15 pd makes it handle like a go cart without a load...

Cheers

[joel0407]

OMG! This thread has become sooo complicated!

Really not sure why sometimes we get bogged down with lots of theory when there are manufacturers specs which set out the proper usage of a product. The pro's and con's of SLS notwithstanding. This member DOESN'T currently have SLS but DOES have a very good system in place to keep his vehicle pretty level (providing that the pressure is lifted to prior to the load)and articulate over most surfaces...... where's the problem?

Fair go mate.

I only bought this vehicle a week ago and I dont have any manual or anything for the Poly Airs. That's why I'm here asking.

I thought it made perfect sense to combine the 2 (SLS and coils). The only thing I misses was that the Poly Airs cant lift the vehicle. I thought I could have the ride and convenince of Air with the reliabilty of Coils.

Through the discussion here I learnt I cant. No need to stress.

As I dont require the back of my Disco to carry much weight so the Poly Airs are pretty useless for me. They wont raise or lower my vehicle, I dont get the more comfortable ride I'm told air gives so I will be just running around with them at minimal pressure. I might as well take them out and sell them.

All the rest of the gear for the original air bags is still there so I might as well take out the springs and sell them with the Poly Airs. Add a few bucks and buy what I need to get the original bags going with a few spares as a fail safe.

Happy Days.

[ozscott]

Fair go mate.

I only bought this vehicle a week ago and I dont have any manual or anything for the Poly Airs. That's why I'm here asking.

I thought it made perfect sense to combine the 2 (SLS and coils). The only thing I misses was that the Poly Airs cant lift the vehicle. I thought I could have the ride and convenince of Air with the reliabilty of Coils.

Through the discussion here I learnt I cant. No need to stress.

As I dont require the back of my Disco to carry much weight so the Poly Airs are pretty useless for me. They wont raise or lower my vehicle, I dont get the more comfortable ride I'm told air gives so I will be just running around with them at minimal pressure. I might as well take them out and sell them.

All the rest of the gear for the original air bags is still there so I might as well take out the springs and sell them with the Poly Airs. Add a few bucks and buy what I need to get the original bags going with a few spares as a fail safe.

Happy Days.

Poly and such will raise the vehicle matey. It will make the ride very firm and the wheel travel poor, but it will raise the vehicle, especially if the springs are a bit tired. If you stick say 25 pound in and dump a load on the back it will not sag. I love the coils with coil helpers - ie aftermarket air bags. The coiler Disco's handled very well from the factory. Many 4wd mags gave them a better ride/handling compromise wrap than the air suspended vehicles. Just keep the bags and springs and go hard!!

Cheers

[vnx205]

Poly and such will raise the vehicle matey. It will make the ride very firm and the wheel travel poor, but it will raise the vehicle, especially if the springs are a bit tired. If you stick say 25 pound in and dump a load on the back it will not sag. I love the coils with coil helpers - ie aftermarket air bags. The coiler Disco's handled very well from the factory. Many 4wd mags gave them a better ride/handling compromise wrap than the air suspended vehicles. Just keep the bags and springs and go hard!!

Cheers

Are you sure some people aren't confusing "raising the vehicle" and "preventing it sagging under load"?

There is a difference.

[ozscott]

Are you sure some people aren't confusing "raising the vehicle" and "preventing it sagging under load"?

There is a difference.

Mine do raise the vehicle unladen over and above the spring height - cant say by how much, but at a guess 1cm, but ride is compromised. Mainly though, you are right, they are to present sag and to throw some (not all of it taken off by the load - for that load bars would be used) of the weight back towards the front

Cheers

[vnx205]

Are you sure some people aren't confusing "raising the vehicle" and "preventing it sagging under load"?

There is a difference.


Mine do raise the vehicle unladen over and above the spring height - cant say by how much, but at a guess 1cm, but ride is compromised. Mainly though, you are right, they are to present sag and to throw some (not all of it taken off by the load - for that load bars would be used) of the weight back towards the front

Cheers

That is right, but it isn't quite the distinction I was trying to make. I would expect that if they were pumped up, that the vehicle would sit a bit higher when unladen. I believe that mine sits a bit higher than standard when I take the camper off the back until I drop the pressure down to about 5psi.

What they don't do well and what the manufacturers don't recommend is putting a load in the vehicle and then pumping the air bags up to try to raise it back to its unladen height. The important difference is when they are pumped up; ie before, not after the load is added.

I know that is only repeating what has already been said. :)

[strangy]

Sorry for a quick detour of the thread.
vnx205 , what weight is your camper packed/ full and what pressure do you run in the bags with the camper on?

Cheers

[vnx205]

The camper is about 360kg empty. So if I add 80 litres of water in the tank, a 9kg gas bottle, about 20 kg for food and about the same for clothes etc, the total is probably getting close to 500kg.

When I fitted them, I put 20 psi in them and that seemed to put my high beam headlights back down about where they should be. It also gave me enough support to maintain the speed I wanted going over the eco drains on the fire trails on the way into Bendethera Valley without bottoming.

Since it seemed to be about right, I must confess I haven't taken careful measurements or experimented with different pressures. So every time I put the camper on, I pump them up to 20 psi. (Before I put the camper on obviously. :D:D )

[wardy1]

Fair go mate.

I only bought this vehicle a week ago and I dont have any manual or anything for the Poly Airs. That's why I'm here asking.

I thought it made perfect sense to combine the 2 (SLS and coils). The only thing I misses was that the Poly Airs cant lift the vehicle. I thought I could have the ride and convenince of Air with the reliabilty of Coils.

Through the discussion here I learnt I cant. No need to stress.

As I dont require the back of my Disco to carry much weight so the Poly Airs are pretty useless for me. They wont raise or lower my vehicle, I dont get the more comfortable ride I'm told air gives so I will be just running around with them at minimal pressure. I might as well take them out and sell them.

All the rest of the gear for the original air bags is still there so I might as well take out the springs and sell them with the Poly Airs. Add a few bucks and buy what I need to get the original bags going with a few spares as a fail safe.

Happy Days.

This wasn't a shot at you mate, not at all! Just sometimes threads go off in tangents and lose the original question. I NEVER get stressed:twisted:
I'd agree that reinstating the SLS is a good thing, just check your compressor to make sure that wasn't the reason for the changeover... they are a bit pricey for what they do really...... All Good:p