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

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.