Why are hoses pre-filled with grease?

In engineering, lubrication lines are pre-filled with grease so that lubrication points are supplied with grease immediately upon initial startup, thereby minimizing dry friction. In addition, a full line provides immediate protection against the ingress of dirt and moisture during storage and assembly.

This method increases the reliability of automatic lubrication systems. Furthermore, it saves a significant amount of time during the initial assembly of a machine. Because machine-filled lines greatly reduce the risk of air entrapment, the system functions correctly and without malfunctions right from the start.

Efficiency and time savings during initial installation

Filling empty hoses and pipes at the installation site itself is a time-consuming process. Especially in central lubrication systems with long pipe runs or dozens of lubrication points, manually pumping grease takes a lot of time.

Filling the hoses mechanically in advance in a controlled workshop environment ensures that this step is completely eliminated at the final installation site. The pre-filled hoses simply need to be installed and connected. This significantly reduces installation time, allowing machines to be put into service faster and lowering installation costs.

What is the risk to system integrity posed by air entrapment?

System integrity means that the installation must always operate reliably and without any loss of performance. Air entrapment poses a major technical risk in this regard. Unlike lubricating grease, air is compressible. When the lubrication pump builds up pressure to transport grease to the bearings, the entrapped air will first be compressed.

Due to this drop in pressure, the progressive manifolds in the system do not switch over correctly. As a result, lubrication points are skipped or receive insufficient grease. The result is metal-to-metal contact, which leads to rapid wear and costly machine downtime. Minimizing air entrapment is therefore essential for the reliable operation of the lubrication system.

The effect of grease viscosity on filling tubes

The viscosity of lubricants, such as Grease EP 2, makes manually filling long, thin polyamide tubes or thermoplastic hoses on site very difficult. Without specialized equipment, this process is extremely labor-intensive and, moreover, difficult to reproduce.

Machine-prefilled hoses ensure that the grease is distributed evenly and without gaps along the entire length. This ensures an immediate and stable build-up of operating pressure as soon as the lubrication system is activated for the first time.

Available types of pre-filled tubes and hoses

Various product groups in the product range are available immediately in a pre-filled (grease-filled) version, tailored to the specific system requirements of the installation:

• Polyamide hoses (PA12): Both the standard PA12 HL and the more flexible PA12 PHLY (such as the 6×1.5 size) are available pre-filled on 50- or 100-meter rolls.
• Polyamide multi-lumen hoses: For systems with parallel lines, bundled polyamide hoses with two or three inner lines are available with grease filling.
• High-pressure hoses: For systems with higher pressure loads, the HPH 4.0×8.6 and HPH 6.3×11.3 models are available pre-filled with grease.
• Thermoplastic hoses: These hoses are supplied pre-filled, using high-quality Grease EP 2 as standard.

Does the pre-filled grease column affect the initial breakaway pressure during a cold start?

Yes, the initial resistance in the line is higher during the very first start than with an empty hose, because grease becomes stiffer at low temperatures (apparent viscosity). However, automatic lubrication systems and manifold blocks are designed to overcome these higher startup pressures (breakaway pressure) without any issues. The fact that the bearings are lubricated immediately from the first rotation is, from a technical standpoint, far more important than the brief, higher pressure spike.

What is the risk of premature oil separation (bleeding) due to mechanical vibrations during transport or downtime?

The risk of premature oil separation is minimized by the filling method and the choice of lubricating grease. Machine-based filling under constant and uniform pressure ensures a homogeneously filled grease column along the entire length of the line. In combination with mechanically stable greases, such as Grease EP 2, the oil remains evenly distributed within the grease, even when subjected to vibrations during transport or downtime.

Need specific advice for a particular application?

Feel free to contact Hydynamic for assistance in selecting the right hose and for more information about material properties.