Jacking Oil Filter DQ6803CA20H1.5C: What Engineers Need to Know Before Reinstallation

The jacking oil filter element DQ6803CA20H1.5C sits at the outlet of the turbine jacking oil pump — a position that makes it more consequential than it might appear on a parts list. Get the installation wrong, and you are not just looking at a small leak. You risk unbuilt system pressure, contaminated oil reaching servo components, and in some configurations, an unplanned outage during the most sensitive phase of turbine startup.

What This Filter Actually Does in a Jacking Oil System

Before a large steam turbine can rotate under its own power, the rotor must be lifted clear of the bearing surfaces using high-pressure oil. This is what the jacking oil system does. It generates enough pressure — typically 10 MPa or higher depending on the unit — to create a thin hydrodynamic film that prevents direct metal contact during slow barring or initial acceleration.

The jacking oil pump outlet filter is the last line of filtration before oil enters that high-pressure circuit. Particles that slip past it can score bearing pockets, clog servo valve orifices, or damage precision actuators downstream. The DQ6803CA20H1.5C uses a 20-micron absolute rating (indicated by the “20″ in the part number) which matches the tolerance limits of most jacking oil system actuators in service today.

The “H1.5C” designation in the part number typically refers to the housing pressure class and connection configuration — details that matter when procuring a replacement, because a dimensionally similar element from a different family may not seat correctly or may not provide the same differential pressure characteristics.

Dual-Filter Housing Configuration: One-Running, One-Standby

In most large turbine installations, the jacking oil system runs two pumps in a one-running, one-standby arrangement. The pump outlet filter element is usually installed within a duplex (twin) filter housing — a configuration that allows one filter to remain in service while the other is isolated for inspection or element replacement, without interrupting oil supply.

How the Duplex Housing Works

A duplex filter housing has a changeover valve — sometimes a rotary ball type, sometimes a sliding shuttle — that redirects oil flow between two parallel filter chambers. When the operator rotates the valve to transfer from Chamber A to Chamber B, the transition needs to happen without pressure drop or oil interruption to the bearing system.

During this switchover, two conditions must be met simultaneously:

• The standby filter chamber must be pre-filled and vented before the changeover valve is turned. Air pockets in an unpressurized chamber create a momentary pressure collapse when oil rushes in.
• The changeover must be deliberate and slow — rapid rotation of the valve can generate a brief hydraulic hammer effect.

Both the running pump filter and the standby filter element should be in good condition. Some engineers overlook the standby element because it is “not in service,” but if a pump trips and the standby activates with a blocked filter, the system may fail to build pressure fast enough to protect the bearings during the transition.

Installation After Overhaul: Where Things Go Wrong

Major overhaul is the most common point at which filter-related problems appear. The housing is opened, the element is replaced (or reinstalled), and somewhere in that process a mistake is made that only shows itself when the system is put back under pressure.

Seal and Gasket Integrity

The element in this series relies on an end-cap seal — usually a nitrile or fluorocarbon O-ring — to prevent oil from bypassing the filter media and flowing directly from inlet to outlet. If this O-ring is pinched during installation, seated unevenly, or left from the previous service without inspection, the result is internal bypass. The system may appear to build pressure normally, but the oil reaching downstream components is unfiltered.

External leakage is more obvious: oil weeping from the housing interface indicates the housing O-ring or cover gasket has failed. After years in service, these seals take a compression set and will not re-seal reliably if reused. Replacing them at every major outage is standard practice, not optional.

Element Seating and Torque

The DQ6803CA20H1.5C element must contact both the inlet port and the outlet tube of the housing correctly. An element that is cocked at an angle or not fully pushed to the bottom of the housing leaves a gap where unfiltered oil can pass. Always confirm the element is bottomed out before tightening the housing cover.

Over-torquing the cover can distort the housing bore slightly, making the seal uneven. Follow the manufacturer’s specified torque — if that figure is not available, contact the supplier before installation, not after.

Bypass Valve Operation: The Risk Nobody Talks About

Most filter housings in this pressure class include a differential pressure bypass valve, typically set to open at around 0.35–0.5 MPa differential. The purpose is to maintain oil flow when the element is severely clogged, preventing pump cavitation or bearing oil starvation.

The problem is that bypass flow is completely unfiltered. If a heavily loaded element causes the bypass valve to open, debris accumulated on the filter surface can be swept downstream along with the bypassing oil.

What Happens Downstream

Servo valves that control turbine actuators have internal clearances measured in micrometers. A single particle above the rated contamination threshold can cause a servo valve to stick, respond sluggishly, or fail in a fixed position. In a turbine control context, that translates directly to speed control instability or loss of steam valve authority.

The bypass event itself is not always loud or obvious. The differential pressure indicator — if installed — may show a return to “normal” range once bypass opens, because the pressure across the element drops. An engineer watching the indicator could reasonably conclude the system is fine when in fact unfiltered oil is now circulating.

This is why scheduled element replacement intervals matter more than condition monitoring alone. Waiting until the bypass indicator trips before replacing the element means you have already operated with degraded filtration.

Replacement Intervals and Condition Monitoring

There is no universal answer for how often the DQ6803CA20H1.5C element should be replaced — it depends on oil cleanliness, system age, and how frequently the jacking oil system is used. Units that start and stop daily will load the filter faster than base-load units in continuous service.

A reasonable approach combines two criteria: a fixed time interval (commonly 8,000–12,000 hours or at each major overhaul) and a differential pressure trigger (typically 0.25–0.3 MPa as a warning threshold, before the bypass valve set point). Whichever criterion is reached first drives the replacement decision.

Oil sampling from the jacking oil circuit — ISO cleanliness class monitoring — provides additional data. A trend toward increasing particle counts between sampling intervals is an early signal that the filter is struggling, even if the differential pressure indicator has not yet alarmed.

Procurement Notes for the DQ6803CA20H1.5C

When ordering replacement elements, confirm these parameters against your housing documentation:

• Filtration rating: 20 micron absolute (not nominal)
• Element outside diameter and length — small dimensional differences affect seal engagement
• End cap seal material: verify compatibility with your oil specification (mineral, phosphate ester, or synthetic)
• Collapse pressure rating — must exceed the maximum pump outlet pressure plus bypass valve set point

Cross-referencing by part number suffix alone can be misleading. Suppliers occasionally revise element dimensions within the same family. Always request a technical data sheet confirming collapse pressure and seal dimensions before committing to a bulk order.

A Few Points Worth Keeping in Mind

The jacking oil filter is a small component in a large system, and it tends to receive attention only when something has already gone wrong. A straightforward policy of replacing both elements in the duplex housing at each major outage, verifying seal condition before reinstallation, and pre-venting the standby chamber before pump transfer will address the majority of failure modes described here.

Bypass valve opening is not a safe fallback — it is a failure mode that happens to preserve oil flow at the cost of filtration quality. Systems with servo valves or other precision actuators downstream cannot tolerate extended bypass operation without consequence.

The DQ6803CA20H1.5C is a precision filter element installed at a critical point in the jacking oil system. Treating it as such — with careful reinstallation, proper sealing, and a defined replacement schedule — is the most practical way to avoid the downstream failures that make turbine startups unreliable.

E-mail: sales@yoyik.com
Tel: +86-838-2226655
Whatsapp: +86-13618105229

Yoyik offers various types of power plants spare parts for steam turbines, generators, boilers as below: