Units, Loads and Movements

This article sets out the conventions the software applies to the values you enter. They are consistent across every support type, and misreading one of them is the most common cause of a result that looks wrong.

Units

The load unit is set per project. Internally the software always calculates in kilograms and millimetres: values entered in newtons are converted on the way in and converted back on the way out, using a standard gravity of 9.807 m/s².

Lengths, travels and variability are never affected by the load unit setting. Variability is a ratio and has no units at all.

The loads

Operational Load (Hot Load)

The load the support carries in operating conditions. This is the primary input and the basis for model selection.

Preset Load (Cold Load)

The load in installed, cold conditions. For variable spring supports you can enter this instead of the hot load — click the lock icon on the datasheet to swap which of the two is the input. The software then works the relationship in reverse.

For constant supports the distinction does not arise: by definition the load is the same throughout the travel.

Hydrotest Load

The load during the pressure test, when the line is full of water. This value is used for checking only. It never selects a model.

The software compares it against the capacity of the load-bearing parts and warns if it is exceeded. A support correctly sized for its operating load can still fail this check — that is what the check is for.

Lateral and axial loads

Horizontal loads, perpendicular to and along the pipe axis respectively. They apply to clamp bases, guides and U-bolts, where the component has to resist them in addition to the vertical load. They are not used to select spring supports.

The movements

Vertical Movement

The thermal displacement between cold and hot conditions, along the vertical axis. This is the only value whose sign the software uses.

• Positive: the pipe rises from installation to operation conditions as a result of thermal movement
• Negative: the pipe falls due to thermal movement

The sign determines the direction of travel and therefore whether the cold load of a variable spring is higher or lower than its hot load. Entering the wrong sign produces a valid-looking result that is wrong in a way no warning will catch.

Lateral and axial movements

Horizontal thermal displacements. The software takes these in absolute value — their direction does not affect the result. They are used to compute the deviation angle of hanging supports and the maximum combined extension of snubbers.

Single and double supports

A double support carries the pipe on two load-bearing elements. The Load Calculations field tells the software how to read the load you entered:

Getting this wrong halves or doubles the design load. It is worth checking explicitly on every double support.

One consequence that surprises people: for clamp bases the relationship runs the other way. The clamp base carries the whole assembly, so in per spring mode the load it sees is twice the value entered. This is not an inconsistency — it follows from what each component actually supports — but it is worth knowing before you compare two numbers on the same datasheet.

Travel Reserves Up and Down

Optional margins that keep the spring away from its end stops. When you define them, they replace the default margins the software would otherwise apply.

They are always taken in absolute value, and each one is optional: define the upper reserve alone and the software applies its default to the lower side.

See Travel and travel reserves.

Max Allowed Variability

The limit above which a variable spring selection is flagged. It can be set for the whole project on the project datasheet, or for one support individually. The individual value takes precedence. If neither is set, the software applies its own default.

Elevations

Top, bottom and middle elevations define the geometry of the installation. From them the software derives the installation height, which drives rod length, the deviation angle and the assembly take-out.

You can also enter the installation length as the top elevation, and leave the bottom elevation blank, if you don’t want to enter the actual elevations.

If the structure elevation comes out below the pipe elevation, the geometry is impossible and the software returns a zero rod length. That is a signal to check your input, not a result.