Oil pressure difference controller FD113ZU Alco Pressure Control

FD113ZU | Oil Pressure Safety Control — 4–65 PSI, 20–150 Second Adjustable Delay, Compressor Protection

Part Number: FD113ZU

Product Type: Oil Pressure Safety Control

Pressure Range: 4–65 PSI (0.3–4.5 bar)

Adjustable Delay: 20–150 seconds (ZU type)

Pressure Connection: 7/16"-20 UNF male

Supply Voltage: 24–240V AC/DC

Reset: Immediate

Protection: IP40

Protection with a Built-In Startup Window

The FD113ZU isn't just a pressure switch — it is a timed safety control designed specifically for compressor lubrication systems. The distinction matters in service. A standard pressure switch that trips the moment oil pressure drops too low will shut down a compressor every time it starts, because pressure takes a few seconds to build from the lubrication pump. The FD113ZU handles this with an adjustable delay from 20 to 150 seconds. The compressor is allowed to start, pressure is given time to establish, and the device only trips if oil pressure fails to reach a safe level within that window.

That startup tolerance is the core of what makes a device like this work in practice. Set the delay too short and you get nuisance trips on cold mornings when oil is thick and pressure builds slowly. Set it correctly and the control does what it's supposed to: ignore normal startup behavior and catch genuine oil-pressure failures that would damage bearings.

The ZU designation in the part number identifies the adjustable-delay version of the FD113 family. Other variants in the series use fixed delays. The 20–150 second range covers the startup behavior of most pressure-lubricated reciprocating and screw compressors.

Practical Details

The 7/16"-20 UNF pressure connection is standard in refrigeration and light commercial compressor packages. The wide voltage range — 24 to 240V AC/DC — makes the FD113ZU compatible with most control circuit designs without any step-down transformer.

IP40 protection is adequate for panel and enclosed-unit installation but is not intended for outdoor or wash-down duty. For harsher environments, the installation location should be reviewed.

Immediate reset means the control resets as soon as oil pressure returns above the threshold — there is no manual reset required after a pressure recovery. This suits systems where the fault clears automatically (such as a brief pressure drop that self-corrects) but means the machine can restart without operator intervention if pressure recovers. Confirm whether the system design expects a manual reset in the event of a trip.

Key Specifications

FAQ

Q1: What is the ZU designation in FD113ZU?

ZU identifies the adjustable-delay version of the FD113 oil pressure safety control. The delay range is 20 to 150 seconds, which can be set to match the oil pressure build-up time of the specific compressor. Other FD113 variants use fixed delays.

Q2: Why does the delay setting matter for compressor protection?

During startup, lubrication oil pressure takes several seconds to build from the pump. A safety control without a startup delay would trip the compressor before oil pressure reaches operating level, causing constant false shutdowns. The delay window allows normal pressure build-up while still protecting the compressor if pressure fails to reach a safe level within that time.

Q3: The compressor trips shortly after startup on cold mornings. Could the FD113ZU delay be set incorrectly?

Yes. Cold oil is more viscous and takes longer to circulate, so pressure builds more slowly on cold starts. If the delay is set at the shorter end of the range and the compressor is in a cold environment, the control may trip before pressure reaches operating level. Increase the delay setting and observe whether the startup behavior changes.

Q4: What happens when the FD113ZU trips?

The output circuit opens, removing power from the compressor control circuit and shutting the system down. With immediate reset behavior, the control closes again as soon as oil pressure returns above the threshold. If the pressure fault has cleared, the system can restart. If the underlying fault persists, the cycle repeats and the problem becomes apparent quickly.

Q5: What should be checked before ordering a replacement FD113ZU?

Confirm the installed part number, verify the pressure range (4–65 PSI) is correct for the application, check the connection thread (7/16"-20 UNF), and confirm the control voltage. Also check the delay setting on the installed unit so it can be matched on the replacement.