Honestly, when I first started managing the procurement of used industrial refrigeration equipment, I assumed the biggest risk was just mechanical wear. I thought if the hours were low and the price was right, it was a good deal. Four years and a couple of very expensive lessons later, I realized my biggest mistake was not having a structured checklist. A bad specification match can cost you more in system redesign than the compressor itself is worth.
This guide is specifically for engineers and plant managers evaluating a used Howden refrigeration compressor—whether it's a screw, reciprocating, or a specific unit like a Howden ČKD compressor from the Košice plant. I review roughly 200 unique items of industrial equipment annually for specification compliance, and I've rejected about 12% of first deliveries in 2023 based on the steps below. Here are the 8 things I check.
1. Confirm the Model and Origin (Not Just the Nameplate)
You'd think this is obvious, but I’ve seen a unit sold as a “Howden WRV 255” that was actually a WRV 163 with a swapped nameplate. It took a 50,000-unit annual order delay to make this my first step.
What to do:
- Locate the serial number. For Howden compressors manufactured after 2001, the serial number links to a specific bill of materials in their system.
- For a unit from the Howden ČKD Košice facility (often stamped on the casing), verify that the parts manual matches the actual configuration. The Košice plant produced specific variants for European refrigeration systems that sometimes have different oil pumps.
- Take a photo of the nameplate. Don’t rely on the seller’s PDF; a blurry photo is often hiding a physical defect.
2. Check the Oil Sight Glass—But Don’t Trust It Completely
This is a step a lot of people skip. They see oil in the glass and assume the lubrication system is fine. A rookie mistake I made was assuming “standard” oil condition meant the same thing to every vendor.
The real check:
- Look for discoloration. Bright amber is good. Dark brown or black indicates severe overheating or potential acid formation.
- Hold a flashlight directly behind the glass. If you see particles shimmering, the oil has metallic content. This means internal wear on the rotors or bearings.
- I'm not 100% sure on this, but in my experience, if the oil looks like used motor oil from a car, the compressor probably needs a full rebuild.
3. Measure the Axial Rotor Endplay (The Step Everyone Ignores)
This is the most overlooked step in the industry. Everyone checks radial play, but axial play in a screw compressor is the killer.
How to do it:
- Remove the inspection port on the discharge end cover.
- Use a dial indicator with a magnetic base. Set it on the male rotor shaft.
- Pry the rotor towards the discharge side, then towards the suction side.
- The tolerance for a Howden screw compressor (WRV / WRC series) should be between 0.05 mm and 0.15 mm. If you see anything over 0.20 mm, the thrust bearings are gone.
4. Rotate the Rotors Manually and Feel for Resistance
Take this with a grain of salt, but I’ve found that the 'feel' of the rotor is often more telling than a vibration analysis report.
The process:
- Use a strap wrench or barring tool on the input shaft. Do not use a cheater bar.
- Rotate the shaft through 360 degrees. You want it to feel smooth and consistent. A 'notchiness' or a spot where it sticks suggests a damaged rotor coating or a seized timing gear (if applicable).
- If the compressor has been sitting for more than a year, the rotors might feel 'sticky' from dried oil film. That’s normal. But if it grinds, that’s rust.
5. Request the Service History (Not Just the Hours)
I used to think that low hours equaled good condition. Now I always ask for the service history.
What to look for:
- How many times the oil was changed. A unit with 5,000 hours and three oil changes is better than one with 2,000 hours and zero changes.
- Ask specifically if the oil filter has been cut open and inspected. A good service tech will do this. If they didn't, the history is incomplete.
- Check if the compressor has ever been exposed to ammonia system contamination (sludge). Look for notes on 'water in oil' or 'witness plate corrosion.'
6. Inspect the Suction Strainer for 'Foreign Objects'
We didn't have a formal inspection process for suction strainers on used units. Cost us when a piece of welding slag from a previous installation went through a brand new compressor.
The inspection:
- Remove the suction screen or filter insert.
- Spread the debris on a white paper towel.
- Metallic chips are bad. Rubber or gasket material is common but a red flag if there's a lot of it.
7. Check the Motor Coupling Alignment
This is often considered a 'site issue' rather than a 'compressor issue,' but misalignment causes premature seal failure.
The quick test:
- If the coupling halves are still attached, check for wear on the flex element.
- If the unit is skid-mounted, use a straight edge across the two coupling faces. An air gap visible anywhere means the motor is misaligned.
- I ran a blind test with our service team: same compressor with proper alignment vs misalignment by 0.5mm. 80% identified the misaligned unit as 'louder' without knowing the difference. The cost increase to fix it on site was about $600 for labor and crane time. On a $18,000 project, that’s 3.3% for measurably better reliability.
8. Verify the Control Panel History (The Digital Check)
Modern Howden units (2015+) have an electronic controller (like the HC300 or a third-party PLC). The vendor who lists all the faults upfront—even if the total looks worse—usually costs less in the end.
What to do:
- Ask for a download of the alarm history. If they can't provide it, that's a red flag.
- Check for frequent 'high discharge temperature' alarms. This indicates poor oil cooling or a bypass issue.
- Look for 'motor overload' trips. This often indicates a mechanical binding issue that has been 'fixed' by resetting the breaker.
Final Note on Pricing and Negotiation
When I placed my first order, I only looked at the purchase price. Now I calculate the 'total cost of re-certification.'
If you find axial play is over 0.20mm in step 3, deduct the cost of a bearing kit (roughly $800 to $2,000 depending on the model) and the labor to do the swap (about $2,500 at a certified shop). That’s your real bargaining chip. The seller probably priced the unit assuming it was 'ready to run.' If it’s not, make them carry the cost.
Honestly, the cheapest quote is almost always the one that costs the most. But the unit with a complete service history and acceptable endplay? That’s the one you buy.
