Gas Springs and Dampers
Frequently Asked Questions

1. Should a Gas Spring be mounted "shaft up" or "shaft down"?

2. Should a Damper be mounted "shaft up" or "shaft down"?

3. What types of end fittings can be used when mounting a Gas Spring or Damper?

4. How does temperature affect the life and performance of a Gas Spring or Damper?

5. What is the expected life of a Gas Spring?

6. How can a designer ensure the longest life for a Gas Spring in an application?

7. I am looking for a gas spring with a 12" of stroke and 20 pounds of force when collapsed.

8. I need replacement gas springs for my car. Do you have them?

Also see our General Frequently Asked Questions.

1. Should a Gas Spring be mounted "shaft up" or "shaft down"?

"Shaft down" is the preferred orientation for mounting a Gas Spring. An optimum design would permit the support to be oriented shaft down through its entire actuation. There are several reasons for this:

In order to achieve the damping or "cushion" at the end of the Gas Spring's stroke, the piston assembly inside of the Gas Spring must travel through oil at the end of the stroke. "Shaft down" orientation ensures that the oil is in the proper location for damping to occur.

"Shaft down" orientation ensures that the shaft and sealing components are lubricated with every stroke of the Gas Spring. This reduces seal wear and helps to inhibit corrosion.

Depending on the application, "shaft down" orientation may reduce the rate of gas permeation through the seal, which increases the useable life of the Gas Spring.

Although inadvisable, Gas Springs may be mounted "shaft up", but this should be discussed thoroughly with an Guden representative.

2. Should a Damper be mounted "shaft up" or "shaft down"?

The type of damping designed into the unit determines the mounting orientation of a damper. Extension and Compression dampers require specific orientations. GUDEN's patented Non-cavitating damper designs can be mounted in any orientation. Extension and Compression dampers should be mounted as follows:

Extension dampers should be mounted "shaft down" to provide consistent damping for the full stroke. If the damper is mounted with the shaft pointing up, the unit may experience inconsistent damping or no damping at all.

Compression dampers should be mounted "shaft up" to provide consistent damping for the full stroke. If the damper is mounted with the shaft pointing down, the unit may experience inconsistent damping or no damping at all. Lubrication of the seal is not a problem due to the high volume of oil contained in a damper.

3. What types of end fittings can be used when mounting a Gas Spring or Damper?

Any type of connector that can be screwed or welded (Gas Springs only) to the shaft and/or body of the Gas Spring or Damper should be suitable for use. When choosing a connector, the designer must take into account both tensile and compressive loading to ensure adequate strength.

The most common connector involves a ball and socket joint. While this joint style is available in many forms, they all allow rotation about the mounting point, which helps to prevent side loading on the support or damper. This is important because side loading can reduce the life of the product.

The simplest connector is a flat welded blade with a through hole. This connector has a low profile and can be very cost-effective, however, side loading can be a concern. This may be addressed by using an oversize hole, which allows for some rotation about the mounting point. Additional concerns with this connector include reduced wear and corrosion resistance.

The designer should also be concerned with the clearance around the mounting point. There should be enough room to easily mount and remove the unit from the application.

4. How does temperature affect the life and performance of a Gas Spring or Damper?

Temperature affects Gas Springs in two ways, output force change and increased susceptibility to gas loss.

As the temperature of the Gas Spring changes, the internal pressure changes according to the relationship P1/T1 = P2/T2. Therefore, as the temperature increases, so does the internal pressure. As the internal pressure increases, so does the output force. For every 10C (18F) change in temperature, the output force changes 3.5 percent.

Very high or very low temperatures can adversely affect the Gas Spring's ability to retain its gas charge. At very high temperatures, the permeability of rubber increases and the gas molecules may diffuse through the seal more quickly. Additionally, rubber compounds may begin to soften at elevated temperatures and lose their ability to seal properly. At very low temperatures, rubber compounds may stiffen and also lose their ability to seal properly. Guden's patented multi-lobe seal design and proprietary rubber compound help to minimize problems at temperature extremes. This allows Guden supports to perform reliably at temperatures ranging from -40C (-40F) to +80C (176F).

5. What is the expected life of a Gas Spring?

When estimating the life of a Gas Spring, one must first determine how much force the support can lose before the application becomes unacceptable. The time it takes to lose this amount of force is considered to be the life of the support.

All Gas Springs lose output force over time. The rate at which force loss occurs varies greatly by application and manufacturer. Many factors affect the rate of force loss, such as: size of the support, orientation, amount of cycles, ambient temperature, vibration, and the geometry of the application. Considering all of the variables, it is very difficult to estimate life accurately without actual testing in the application.

As noted above, all Gas Springs will lose output force over time. It is recommended that the supports be periodically checked to ensure that they are functioning as intended. This inspection should be implemented as part of a planned maintenance activity, if possible.

6. How can a designer ensure the longest life for a Gas Spring in an application?

Orient the support "shaft down". As explained above, this will continually lubricate the seal and shaft and reduce permeation through the seal.

Utilize the largest gas volume possible in the support. In general, use the minimum stroke required with the largest body possible. In a support with a large gas volume, small gas losses are imperceptible in the output force. The temperature of the Gas Spring should remain well within the temperature limit s. If temperature extremes will be encountered, it should be for a short duration and the support should not be cycled while at the extremes. Utilize the highest force Gas Spring possible that still provides acceptable handle loads for the application. This will allow for some force loss without the loss of function of the application.

Provide multiple mounting locations so that the support can be moved to accommodate for force loss as the support ages.

7. I am looking for a gas spring with a 12" of stroke and 20 pounds of force when collapsed.

Please visit our stock gas spring pages http://www.guden.com/dampers.htm to compare the sizes available to the size you require. If you do not see the exact size please contact a Customer Service Representative for the availability and pricing of a custom gas spring size.

8. I need replacement gas springs for my car. Do you have them?

We don't stock direct replacement gas springs for cars, but you can find them through either J.C. Whitney or NAPA; Search for "lift supports." You can also visit a nearby auto parts dealer.