When Your Homogenizer Won’t Build Pressure
A homogenizer that fails to reach or maintain operating pressure is one of the most common — and most costly — problems in production. Every minute of unplanned downtime affects output, product quality, and delivery schedules. This diagnostic checklist helps maintenance engineers systematically identify and resolve pressure issues on Gaulin, APV, Rannie, SPX, and BOS homogenisers.
Work through these checks in order. The most common causes are listed first.
1. Inspect the Homogenising Valve Assembly
The homogenising valve is the component that creates back-pressure in the system. If the valve seat or valve stop is worn, damaged, or incorrectly assembled, the machine cannot build pressure.
What to check:
Remove the valve assembly and inspect the valve seat and valve stop for scoring, pitting, erosion, or uneven wear patterns. Even minor surface damage can prevent proper sealing and cause pressure loss. Check that the valve and seat are correctly aligned and that the impact ring (if fitted) is not worn beyond tolerance.
Action: Replace worn valve components. BOS stocks valve seats and stops in Stellite, Tungsten Carbide, Ceramic, and Diamond Coating for all major brands. Consider upgrading to a harder material if valves wear frequently.
2. Check Plunger Packings for Leaks
Plunger packings seal the high-pressure cylinders. When packings are worn, product leaks past the plungers and the machine cannot maintain pressure. Visible leakage around the plunger area is the most obvious sign, but even small internal leaks can cause significant pressure loss.
What to check:
Look for product dripping or spraying from the packing area during operation. Check the packing condition — hardened, cracked, or compressed packings must be replaced. Verify that the packing gland is correctly tightened. Over-tightening can cause premature wear; under-tightening causes leaks.
Action: Replace the complete packing set. Always replace all packings simultaneously, never individually. BOS supplies plunger packing kits for Gaulin, APV, Rannie, and SPX homogenisers with same-day dispatch available.
3. Examine the Suction and Discharge Valves
The suction (inlet) valves and discharge (outlet) valves control product flow into and out of the compression cylinders. Worn or stuck valves allow product to flow backwards, reducing effective pressure.
What to check:
Remove and inspect each suction and discharge valve. Check valve seats for wear, pitting, or product build-up. Verify that valve springs have correct tension — weak springs cause valves to close too slowly. Check that O-rings and seals are intact. Listen for abnormal clicking or hammering sounds during operation, which can indicate valve problems.
Action: Replace worn valves and springs as a set. Ensure valve seats are flat and undamaged. BOS supplies complete valve kits including springs and seals.
4. Verify Drive System and Crankcase
If the compression end components are in good condition but pressure is still low, the problem may originate in the drive system. Insufficient plunger stroke, incorrect speed, or mechanical issues in the crankcase can all affect pressure generation.
What to check:
Verify that the motor is running at the correct speed — a VFD set too low will reduce pressure. Check belt tension if the machine uses belt drive. Inspect the crankshaft, connecting rods, and crossheads for wear or play. Excessive clearance in these components reduces the effective plunger stroke.
Action: Adjust motor speed to specification. Replace worn drive components. For BOS MG series machines, consult the operating manual for correct speed settings.
5. Check Oil Pressure and Lubrication
Many homogenisers use an oil pressure system to control the homogenising valve. Low oil pressure directly translates to low homogenising pressure. Additionally, inadequate lubrication of moving parts causes accelerated wear that leads to pressure loss over time.
What to check:
Read the oil pressure gauge — it should match the specification in your operating manual. Check oil level in the crankcase and hydraulic system. Inspect the oil for contamination (milky appearance indicates water ingress, dark particles indicate wear). Verify the oil pump is functioning and that oil filters are not blocked.
Action: Top up or replace oil as needed. Replace oil filters. If the oil pump is faulty, replace it. Use only the oil grade specified by the machine manufacturer.
6. Check for Air in the System
Air trapped in the product line or compression cylinders prevents the machine from building full pressure. Air is compressible, unlike liquid, so even small amounts dramatically affect performance.
What to check:
Ensure the feed tank has sufficient product level — a low level can cause the pump to draw air. Check all inlet connections for leaks that could allow air ingress. Verify that the feed pump is priming correctly. Bleed the system if air pockets are suspected.
Action: Eliminate air ingress points. Ensure adequate feed pressure and product level. Run the machine at low pressure initially to purge air before increasing to operating pressure.
7. Verify Pressure Gauge Accuracy
Before assuming a mechanical fault, confirm that your pressure readings are accurate. A faulty pressure gauge can make a correctly functioning machine appear to have a problem.
What to check:
Compare readings with a calibrated reference gauge. Check for a blocked or damaged gauge connection. Glycerine-filled gauges should not show air bubbles or leaking fluid.
Action: Replace or recalibrate faulty gauges. BOS supplies pressure gauges for all major homogeniser brands.
Still Can’t Resolve the Issue?
If you have worked through this checklist and the problem persists, the issue may require specialist diagnosis. BOS provides on-site service in the Netherlands, Belgium, and Germany, and works with qualified service agents worldwide.
Contact BOS with your machine model, serial number, and a description of the symptoms. Our engineers can often diagnose the issue remotely and arrange the correct parts for immediate dispatch.
BOS Homogenisers B.V. — +31 35 621 3190 — sales@boshomogenisers.com
Related Guides
- How to Replace Plunger Packings on a Homogeniser
- 5 Signs Your Homogeniser Valve Needs Replacement
- Compare Valve Materials: Stellite vs Tungsten Carbide vs Ceramic