White Paper Dry Couplings

1. Introduction

2. Types of Dry Couplings

Dry couplings are available in various designs. They can generally be divided into quick coupling systems and industrial dry couplings.

Quick coupling systems (such as plug couplings) can be quickly and safely connected or disconnected manually. These are used in pneumatic, hydraulic, or hydrogen applications. A classic example is the compressed air safety plug coupling, which is used in nearly every compressed air system.

Industrial dry couplings, on the other hand, are often used for hose lines and tank systems with nominal sizes ranging from ¾“ to 6“.

Depending on the manufacturer and application, there are various constructive variants:

Manufacturers use different geometries, so these are usually not combinable with each other. This type is used in the chemical and pharmaceutical industries, especially if an internal control curve might be hindered by possible contamination, such as abrasion.

Dry coupling with a ball valve that shuts off on both sides:

This variation of the dry coupling opens the full relieving cross-section, allowing for the dry connection and disconnection of highly viscous and crystallizing-prone media.

STANAG Couplings:

STANAG stands for Standardization Agreement, a standardization agreement of NATO member states regarding the application of standardized procedures or similar equipment.

STANAG couplings are issued by the NATO Standardization Office (NSO). Couplings of this type follow the STANAG 3756 standard and are compatible with each other regardless of the manufacturer. The main area of application is fluid handling for chemical and petrochemical products, for example, during tank car unloading.

3. Materials

4. Design and function description

A dry coupling essentially consists of two components:

System Unit (tank unit, socket)
Hose Unit (hose unit, plug)
Both the hose and system units have an internally located valve cone, which is secured and sealed in the dry position by corresponding valve springs.

When connecting the two units, the corresponding valve seat of the hose unit and the valve cone of the system unit are axially shifted by a rotary motion, allowing the valves to release a corresponding flow cross-section (bayonet closure). When the connection is loosened, the internal valve springs return the valve seat and valve cone to the sealing and dry position.

The mechanical connection of both units can (as in types of dry couplings) occur through different functional principles.

In STANAG couplings, both units are connected via rotary motion with internal curve guidance.

Both the mechanical connection and the retraction of the valve cone/seat require a certain amount of force, which may vary depending on the manufacturer. Therefore, handles are used for nominal sizes from DN 50 and up.

Additionally, all mother part dry couplings (hose unit) are equipped with a swivel joint to avoid possible torsion of the hose line.

5. Nominal Sizes

6. Pressure Loss KV/CV Value

7. Coding

At loading stations, several hose lines are often used side by side and simultaneously.

To prevent a hose line from being connected to the wrong system unit—which could lead to media contamination and even serious accidents (mixing reactive media)—various coding systems are employed.

The simplest variant is color coding on the hose and system unit, such as different colors of the handle up to the color-coated coupling on both sides. A 4-eye principle for work safety is highly recommended.

The safest mechanical variant is a coding system where specific “key/groove” geometries are integrated into the end faces of the hose and system unit.

This ensures that the hose unit can only be coupled to a specific system unit. The number of possible codings depends on the nominal size of the dry coupling. It should be noted that a non-coded mother part (hose unit) can still fit onto any coded father part (tank unit).