The three parts that make the seal
A compression fitting has three pieces: a body, a nut and a ferrule, which is the small ring also called an olive. The pipe slides into the body through the nut and the ferrule. As you tighten the nut, it forces the ferrule to wedge between the nut and the tapered end of the body.
That wedge squeezes the ferrule onto the outside of the pipe. The ferrule bites into the copper just enough to hold, and it fills the gap between pipe and body so water cannot pass. No heat is involved.
The seal depends on a clean, round pipe end. Even a small gouge or an oval pipe can leave a path for water.
How to make a good compression joint
Each step matters. Skipping any one is the usual cause of a weeping joint.
- 1
Cut square
Use a tubing cutter, not a hacksaw. A square, clean end seats flat.
- 2
Deburr and clean
Ream the inside edge and wipe the outside of the pipe until it is shiny.
- 3
Slide parts on in order
Put the nut on first, then the ferrule, with the long side facing the body.
- 4
Seat and tighten
Push the pipe fully into the body. Hand-tighten, then add about one to one and a half turns with a wrench.
- 5
Test slowly
Open the water gradually. Wipe the joint dry and watch it for several minutes.
A second wrench on the body keeps it from twisting and straining the pipe behind it. Do not wrap tape or add sealant on the ferrule unless the maker's instructions say to, because it can stop the ferrule from seating.
Compression fitting or sweat solder
Both join copper. They suit different jobs.
Compression fitting
- No torch, so no fire risk near wood
- Can be disassembled and tightened
- Works where the pipe cannot be fully drained
- Bulkier and less forgiving of poor prep
Soldered joint
- Permanent and compact
- Fits inside walls and tight spaces
- Needs a dry pipe and a torch
- Takes more skill to do cleanly
Fitting dripping under the sink?
Our line is answered 24/7. Licensed and insured plumbers, clear price before work starts.
Where a compression fitting makes sense
These are the situations where we are comfortable with one.
Fixture shutoff valves
Angle stops under sinks and toilets connect to 3/8 inch supply lines with compression nuts. These are designed for it.
Accessible repairs
A fitting you can see and reach is easy to check, so a slow weep is spotted early.
Pipe that cannot be drained
Where a line cannot fully dry for soldering, compression lets you make the joint without steam ruining it.
Connecting different materials
Transition fittings join copper to other pipe types without a torch.
Where we do not use compression fittings
Compression fittings are not for every location. We avoid them in these cases:
- Inside walls, ceilings or floors where a leak would go unseen
- Under or inside a concrete slab
- Buried service lines, where soil movement stresses the joint
- Lines that vibrate or flex, such as near a pump or a water hammer arrestor
- Gas lines, which have their own rules and need a licensed plumber
Scale, hard water and compression joints in Midvale
Jordan Valley Water Conservancy District reported total hardness in 2025 at an average of 182.4 mg/L, with a range from 16.0 to 381 mg/L. The USGS calls water above 180 mg/L very hard, and 182.4 mg/L is about 10.7 grains per gallon. That figure describes JVWCD water, which feeds the east side of Midvale. West-side homes get city well water, so ask Midvale Public Utilities for the annual water quality report.
Hard water leaves mineral crust on the outside of fittings wherever there is even a small weep. A bit of white or green crust at a nut is a sign that water has been getting past the ferrule. It also glues the nut to the body so that it seizes the next time you try to loosen it.
Scale does not make a good compression fitting fail, but it does hide a bad one. If you see crust, wipe it off, tighten the nut a small amount and watch for a day. If it keeps weeping, replace the fitting rather than cranking on the nut. You can also test your tap with hardness strips to see how much scale your water carries.
Common compression joint problems
Most trouble comes from prep or overtightening.
| Problem | Likely cause | What to do |
|---|---|---|
| Drip from the nut | Under-tightened or ferrule not seated | Tighten a quarter turn, then recheck |
| Leak after tightening hard | Crushed ferrule or oval pipe | Cut off and replace the ferrule |
| Green crust on the joint | Slow weep and mineral build-up | Clean, retest and replace if it returns |
| Nut will not budge | Scale or corrosion | Soak in vinegar and use two wrenches |
| Leak from a reused joint | Ferrule already deformed | Use a new ferrule every time |
Honest limits
Compression fittings are not a long-term fix for a failing pipe. If you are patching copper that is pitted, thin or corroded from the inside, the next leak will show up next to the one you just fixed. In that case a full repiping plan is the better direction.
They also do not belong on the main water line to the house. Midvale says service laterals typically belong to the property owner, and a lateral failure is a job for a licensed plumber. Our water line repair page explains the options for that.
When to call a pro
Call a licensed plumber if a joint will not stop weeping, if the pipe is hard to reach, or if you have to cut into a wall. We also handle any work that touches the main shutoff. Midvale Public Works at 801-567-7235 handles water emergencies on the city side of the meter.
We serve homes across Midvale and nearby towns, including Sandy.
Where this guidance comes from
Fitting use follows the International Plumbing Code (IPC) and the fitting maker's guidelines for torque and pipe prep.
Compression fitting questions from Midvale homeowners
In the right place, yes. On accessible fixture connections with clean prep and correct tightening, they last for years. In hidden or high-vibration spots, they are a poor choice.
The nut and body can be reused, but the ferrule is deformed once tightened and should be replaced. Reusing it is a common cause of leaks.
They work on rigid and soft copper of the matching size, but soft copper may need an insert. Check the maker's instructions.
Not directly, but scale builds up at any weep and can seize the nut. JVWCD water averaged 182.4 mg/L hardness in 2025, so expect some scale in the east side of Midvale. Ask the city about well water on the west side.
Hand-tight, then about one to one and a half turns with a wrench. Over-tightening crushes the ferrule and causes the leak you are trying to prevent.
Do not. Gas piping has its own rules and should be done by a licensed plumber. If you smell gas, leave the building and call Enbridge Gas at 1-800-767-1689 or 911.