Isohitech Positive Injector Systems

What Is a Positive Injector Lubrication System?

A positive injector lubrication system (PDI — positive displacement injector) delivers a fixed volume of oil or soft grease to each bearing on every lubrication cycle. Unlike restrictor-based single-line systems, each injector is a small positive-displacement valve: when main-line pressure rises, internal pistons shift and discharge a metered dose; when pressure falls, injectors recharge from the supply line for the next cycle.

PDI systems typically operate at low to medium pressure (roughly 12–45 kgf class on common models, up to higher classes on SL1/BL series). They are ideal when different friction points need different ml/cycle on the same circuit — machine tool slides, packaging lines, injection molding tie bars, and conveyor bearings are typical applications.

How a PDI Cycle Works

1. Pump starts — timer, PLC, or machine interlock energizes hand pump, auto reservoir pump, or central power station.
2. Pressure builds — lubricant fills the main line; each injector charges until its cracking pressure is reached.
3. Injectors fire — pistons stroke in sequence or parallel (layout-dependent), discharging the rated ml/cycle at each point.
4. Pressure reliefs — pump stops or relief valve opens; line pressure drops and injectors reset.
5. Idle interval — controller waits for the next cycle; bearing film carries load until the following dose.

Correct cycle time is critical: if the interval is too short, not all injectors complete; if too long, bearings may run dry between doses.

Key Advantages of Positive Injector Systems

• Precise lubrication delivery — repeatable dose per injector model, not dependent on line length alone
• Customizable per point — mix Single, ZEM, DLX, SL1, or BL injectors on one manifold for different ml/cycle
• Modular expansion — add injectors to the main line without replacing a progressive metering block
• Low to medium pressure — simpler tubing and fittings than 20–30 MPa progressive grease circuits
• Easy monitoring — visual pin movement or cycle indicators show which injectors are active
• Cost-effective — lower installed cost than dual-line for moderate point counts with variable dosing needs

PDI vs Single Line vs Progressive vs Dual-Line

Deep dive: PDI vs single-line technical comparison.

Typical System Components

1. Pump — high pressure hand pump (manual routes), 1–4 kg auto pumps (timed cycles), or power station for 500+ point class systems
2. Main supply line — 6–10 mm nylon or copper; clip every 300–500 mm with lubrication pipe clips
3. Injectors — see selection table below and product slider on this page
4. Controller — built-in timer on auto pumps or external PLC; set minimum cycle time for full injector stroke
5. Accessories — pipe & tubing, brass straight/elbow fittings, chain brushes, manifolds

Injector Model Selection Guide

Pump Pairing Guide

When to Choose PDI — and When to Choose Something Else

Choose positive injector when:

• Points need different ml/cycle on the same pump circuit
• You lubricate with oil ISO #20–1500 or soft grease NLGI 000–00
• You want to add points later without resizing a progressive block
• Pressure class stays in low to medium range for most injectors

Consider Lincoln SSV progressive or VSG dual-line instead when:

• Chassis or heavy equipment needs NLGI #2 grease at 20–30 MPa
• Point count is high and sequential progressive metering is preferred over individual injectors
• Plant size requires alternating dual mains over long distances

Industry Applications

• Machine tools — way oils to slides, ball screws, and spindle bearings via oil PDI
• Injection molding — tie-bar and hinge points on 24/7 cycles with light grease injectors
• Packaging & conveyors — chain and roller bearings; pair with brush accessories where needed
• Textile & printing — many small oil points with adjustable ZEM/DLX injectors
• Food & beverage — stainless fittings and food-grade oil where required (specify on quote)

Installation & Commissioning Checklist

1. Count active lube points and target ml/cycle per point.
2. Select injector model per point; sum peak flow for pump sizing.
3. Route main line with minimum bend radius and clips per pipe fittings guide.
4. Set controller cycle interval long enough for all injectors to complete one stroke.
5. Prime system — run 3–5 cycles; verify fresh lubricant at every point.
6. Label injectors and lines with point ID matching maintenance records.

Troubleshooting Quick Reference

Maintenance Schedule

• Weekly: visual check — reservoir level, leaks at fittings, injector pin movement
• Monthly: verify cycle counter or timer; inspect clips and rub points on tubing
• Quarterly: sample one injector per circuit — disassemble, clean, replace Viton/NTR seals if cracked
• Annual: flush main line if oil oxidation or grease separation observed; recalibrate timer to production hours

Request a full bill of materials: contact IsoHiTech for a quote with point count, lubricant type, cycle interval, and environment (indoor, washdown, mobile).

Before you buy: read our grease fitting types guide.

Frequently Asked Questions