Low pressure air bags

[firefighter4u]

Our dept. is looking into purchasing low pressure air bags instead of high pressure. Does anyone have any comment on how well they work, problems, etc.?

[unit3sfd]

my dept. uses high pressure bags now. but we have added a new high pressure bag that lifts similar to a low pressure bag, but allows us to connect them together. and lift the high ton loads as well best thing weve used in a while. you can e-mail me at hotmail unit3sfd, or sullfire@viaduct.custom.net

[e33]

There are very vast differences in the way that hi and low presure bags operate. If you are planning to buy the lo pressure bags instead of hi pressure ones, rethink your position. Hi pressure bags are designed to lift greater capacities smaller distances. The factor that is critical to the lift is the surface area of the bag. You will find that lo pressure bags will lift their rated capacity the full spectrum of their height. While a high pressure bags capacity will diminish as it rises. For example..a Paratech k-74 bag is rated as a 73.5 ton bag...it will only lift this load approx 1". It will lift 70 tons slightly higher...etc....since the surface area of the bag diminishes as it rises...it loses capacity. The advantage of a low pressure bag is that it will lift the same capacity through its full range of height. They also conform better to the object being lifted and are good for use on curved and irregular surfaces. Their height is also a great advantage. The neat thing is that you are only dealing with anywhere from 7-10 psi. If the hose should come disconnected...you can stop the flow with a single hand over the air port. They both have their uses...i would say that you should buy both kinds to be able to handle all types of lifting.

[This message has been edited by e33 (edited March 22, 1999).]

[firefighter4u]

Thanks for the info. The main reason that we are looking at the low pressure is that a nearby dept. has a full range of high pressure bags and thought we might complement them with low pressure bags. What is the capacity of a low pressure bag? And is there much of a price difference?

[This message has been edited by firefighter4u (edited March 22, 1999).]

[DQuinn]

Our dept. has only low press bags and we have been pushing to get high press. The lows, as stated above, do have their applications, especially in conforming to the required shape, both the vehicle and the surface below. However the greatest drawback we have encountered is their increasing instability the more the lift distance increases. As the bag goes up, if you are not entirely level, or just due to the ravel of the vehicle on its axis, it will want to shift to the side, sometimes necessitating reseting the lift. It's kind of like a tire with a real soft sidewall.

Both have their place, but after experimenting, we feel better using the high press. in most applications. It's another case where you should really try before you buy.

[rshaw]

As a suggestion to which airbag might be right for your department, try looking up the NT Airbags. The new tech. rescue airbags combine the best of both features. High lift, high pressure, and they are stackable.

Each bag can be inflated separately or interconected (1 of 3; 2,of 3; or 3 bags together). There is a threaded adapter between the bags, with either an open adapter or a plug to isolate the bags. The stackability feature gives the height of the low presure airbag, but with the advantage of high pressure airbags. The surface area in contact with the object to be lifted does not change, so the lift is constant. This is the disadvantage of the high pressure airbag; as the lift increases, the surface area decreases. The simple formular of surface area times operating pressure at one inch will give you the a bag's lift rating(WxLxP=Lift).

As you inflate a high pressure bag to increase the hdight, you decrease the lifting capacity by reducing the surface area. As the bag inflates beyond its rating of 1 inch in height, the surface area in contact with the object now decreases. The bag rounds out, as it does the surface area gets smaller.

Conversely, the surface area of the Low pressure rescue airbags remain consistent as the bag is inflated.

The surface area of NT Rescue airbags also remains constant as the mutiple cells are in flated.

Code 3 makes one type as described above, Hurst and other companies have all developed NT rescue airbags. Run through Firehouse and you will find a picture describing them.