In any efficient and reliable lubrication system, oil cleanliness is a core factor affecting equipment lifespan and operational efficiency. Strainers, as the front-line filtration devices in lubrication systems, play a critical role in pre-filtration. However, engineers and operators often raise the following questions: Can oil pass through strainers smoothly? What exactly is the function of a strainer? How does it differ from subsequent fine filters?

This article systematically explains the role of strainers in lubrication systems, covering their working principles, pre-filtration objectives, and practical applications across different systems.

1. Can Oil Pass Through a Strainer?

Answer: Yes, but with limitations.

(1) Strainer Structure Allows Oil Flow

A strainer is fundamentally a low-precision filter made of stainless steel mesh or perforated metal plates. It features uniform pores, typically sized between 80–500 μm (micrometers), allowing most clean oil to flow through unimpeded.

(2) Contaminants Are Blocked

Particles such as metal shavings, seal fragments, and carbon deposits in the oil are intercepted by the strainer, preventing them from entering the oil pump or other critical components.

(3) Oil Temperature and Viscosity Affect Flow Efficiency

Low temperatures or high-viscosity oil may reduce flow rates or even cause blockages. This is one reason for low oil pressure during system startup.

2. Objectives and Significance of Pre-Filtration

(1) Protecting the Oil Pump

Internal pump components (gears, impellers, or plungers) are highly sensitive to solid particles. Pre-filtration prevents particles from entering the pump, avoiding premature wear or seizure.

(2) Reducing Load on Primary Filters

By intercepting large contaminants, strainers allow primary filters (e.g., oil filter cartridges) to focus on finer impurities, extending their service life and maintaining stable system flow.

(3) Lowering System Failure Rates

Pre-filtration reduces risks such as pump failure, orifice blockages, and lubrication breakdown caused by foreign particles, enhancing overall system reliability.

3. Typical Applications of Pre-Filtration Devices

4. Design and Usage Considerations for Strainers

(1) Pore Size Selection Must Align with System Precision Requirements

80–100 μm: Typical for engine oil systems.

150–300 μm: Used in hydraulic equipment.

>400 μm:  Suitable for low-pressure or open-loop systems.

(2) Set Cleaning Cycles According to Operating Conditions

Harsh environments or new equipment break-in periods: Clean every 200 hours.

Normal operating conditions: Clean or replace during oil change intervals.

(3) Avoid Over-Reliance on Strainers as Fine Filtration

Strainers only provide primary filtration and cannot remove fine particles or emulsified contaminants. They are not substitutes for fine filters (e.g., spin-on oil filters).

5. Common Causes of Restricted Oil Flow Through Strainers

6. Q&A

Q1: What is the difference between a strainer and a filter cartridge?

A1: Strainers are primarily used for coarse filtration at the suction side, are generally reusable, and can be cleaned. Filter cartridges are installed on the pressure side for fine filtration, offering higher precision but are typically disposable.

Q2: Can a strainer be omitted?

A2: Not recommended. Strainers effectively prevent particles from entering the oil pump. Removal may lead to pump damage or even system shutdown.

Q3: Should seals be replaced during strainer cleaning?

A3: It is advisable to inspect the sealing ring for aging or deformation. Replace if damaged to avoid air or oil leaks.

Q4: Can increasing the strainer’s mesh density improve filtration?

A4: Theoretically yes, but excessively dense mesh may restrict oil flow, create vacuum pressure, or induce cavitation. Carefully evaluate the system’s allowable pressure drop before implementation.