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How To Fix A Leaking Door Closer

How To Fix A Leaking Door Closer

A door closer is a device that uses a combination of closing spring power and hydraulic fluid regulation to safely close a door in a controlled manner. One of the most common problems with a door closer is when it begins leaking oil. In this article we explain why a door closer leaks oil and how to repair a door closer that is leaking oil.

How A Hydraulic Door Closer Works

To understand how to fix a leaking door closer, it is best to first understand how a hydraulic door closer works. A hydraulic door closer consists of a closer body, typically made of cast iron, or aluminum. The door closer body houses the door closer's rack and pinion design and internal spring.

Opening Cycle

The pinion gear is illustrated below. At the bottom of the pinion is the arm spindle where the door arm attaches. The pinon gear sits perpendicular to the rack gear and meshes with it. The rack gear sits directly beside the spring. As the door opens, the spindle and pinion assembly rotates, causing the rack gear to slide towards the spring and compress it.

Closing Cycle

When the person passes through the door way, the spring decompresses, pushing the rack gear back to it's original position, causing the arm spindle to rotate back, causing the door to close.

The spring, rack gear, and pinion gear contribute to the opening and closing cycles of the door closer. However, there is another major component to door closers and that is the hydraulic aspect. Hydraulics are used in door closers to regulate the door closing speed or dampen the closing. Let's explore how this works.

Hydraulics and Door Closers

Hydraulics are used in a vast array of applications including commercial door closers. The main idea of hydraulics deals with the properties of liquids. Unlike gases, liquids can't be compressed. A great example of this is a medical syringe as illustrated below. A syringe is comprised of plastic cylinder known as the barrel which holds all the liquid. A plunger is located at one end of the barrel, while a small needle is located on the opposite end. The needle is hollow and this is where the liquid exits the barrel. When a nurse uses the syringe he or she pushes on the plastic plunger with their thumb using force. As the plunger pushes down into the barrel, we know that liquids do not compress. As a result the liquid has to move so it is forced through the small needle hole. When the liquid is forced through the smaller hole, it comes out at high speed since it cannot be compressed. The hydraulics in a door closer act in a similar manner in order to regulate the speed of the door closing.

A door closer body is filled with hydraulic fluid. Inside the door closer body are 2 cylindrical bored holes. There is a large horizontal cylindrical bored hole which houses the spring and rack gear and there is a vertical bored hole which houses the pinion gear and spindle assembly. Hydraulic fluid fills the entire door closer body.

The rack gear acts very similar to a piston in a car engine. The rack gear itself is a cylindrical shape. It is designed to move back and forth along the horizontal bored hole in the closer body. The tight tolerances of the rack gear allow no hydraulic fluid to pass inbetween. Similar to a piston head, that is used to compress gas inside of the engine's cylinder.

With the rack gear in place, hydraulic fluid must be able to travel on both sides of the rack gear since we know that hydraulic fluid cannot be compressed. This is accomplished by small, tiny channels in the closer body that connect to both sides of the rack gear. A hex key screw valve is connected to each channel. The valve can be opened or closed in order to regulate the size of the channel that the hydraulic fluid passes through.

Here Is How The Speed Regulation Works

When the door opens the spring compresses, forcing all of the hydraulic fluid into the rack side of the gear. When the door begins to close, the spring begins to decompress back to normal length. As the spring decompresses it pushes on the rack gear similar to a piston. As it pushes on the rack gear, since hydraulic fluid cannot compress, it is forced through the tiny channel into the spring side of the closer body. The valves that connect to the small channels can be opened to increase the closing speed, or closed to decrease the closing speed.

Hazards Of Door Closer Leaking Oil

Staining Door Finish or Veneer

Oil can be very messy, and if you have ever changed the oil in a car, you understand this. If a door closer is leaking oil, it can run down the entire face of the door, staining and ruining the door surface. If the door is a hollow metal steel door with a primed gray finish, oil will destroy the primer. Likewise, if this is a commercial birch veneer door, oil will stain the veneer finish.

Slip Hazard

If a door closer is leaking oil, and remains leaking oil for a long period of time, the oil can eventually run down the entire door and onto the floor. Oil can be very slippery and having it on the floor unbeknownst to pedestrians passing through the doorway can be very dangerous, especially if the pedestrians are young children, the elderly, or people with disabilities. If a pedestrian does step on the oil and manages not to slip, they will then be tracking the oil on their shoes throughout your entire building potentially causing even more damage to carpeted, tile, or hardwood floors.

Non-functioning Door Closer

The hydraulic fluid inside of the door closer is used to dampen the closing speed during the closing cycle. With insufficient fluid in the door closer body, the door closer can slam shut since there is no resistance when the internal spring decompresses.

Causes For A Leaking Door Closer

Defective O-Rings Seals

As explained previously, hydraulic fluid travels between both sides of the rack gear through small channels. Each small channel is connected to a hex key screw type valve with an O-Ring. If the O-Ring is compromised or damaged in any way, the door closer body will no longer be sealed, and hydraulic fluid will leak from the valve.

Incorrect Adjustment

All commercial door closers feature 2 valves to control the closing or sweep speed and the latch speed. It is always recommended that when making adjustments to only rotate the hex key screw 1/8 to 1/4 turns at a time. One of the most common reasons the door closer leaks oil, is from the installer's own negligence by simply unscrewing the valve all the way. If the valves are unscrewed too far, oil will immediately leak from the channels.

Backcheck Valve Completely Closed

Backcheck is a valve that controls the opening speed of the door closer during the 75 degree to 90 degree opening range. The backcheck valve should never be closed all the way. If done, the door closer will not be able to fully open, and if done will put excessive pressure on the backcheck seal. Improper adjustment could result in damaging the backcheck seal.

Identify Door Closer Leak

Analyze where the door closer is leaking hydraulic fluid. Because hydraulic fluid is dark (looks like oil), it is easy to identify where the oil is leaking from. In most cases the oil leaks from a location where there is a seal. Common door closer hydraulic fluid leak locations include the valves or pinion/arm spindle.

Replace The Seals

Once the leak is identified, the component will need to be removed from the door closer in order to replace it. Carefully remove the door closer from the door and place it in a vise.

Valve O-Ring Replacement

Remove the hex key valve screw by completely unscrewing it from the door closer. Be sure the door closer is placed in the vise, so oil will not pour out of the door closer. Remove the O-Ring from the bottom of the valve screw and install the new one. The door closer will now need to be filled with more oil, depending on how much oil was lost.

Pinion / Arm Spindle O-Ring Replacement

In order to remove the pinion O-ring seal, the entire pinion and arm spindle will need to be removed. The actual seal sits inside of the closer body, but in order to access it the pinion and arm spindle assembly must be removed.

Closer Body End Cap O-Ring Replacement

At each end of the door closer are end caps, that can be removed using special door closer wrench. The end caps have O-Rings which can be replaced.

How Do You Fill A Door Closer With Oil

If the door closer was leaking oil and all proper O-Ring seals have been replaced, new hydraulic fluid can be replenished into the door closer. Before beginning always make sure you have the proper safety equipment including safety glasses and gloves.

1. Place the door closer vertically in the vise so that the "S" Sweep and "L" latch valves are visible.

2. Remove the end cap from the door closer body.

3. Slowly poor hydraulic fluid into the door closer body. IMPORTANT: Be sure to wear safety glasses, as hydraulic fluid can squirt out.

4. As the hydraulic fluid is poured in, slowly rotate the door closer arm. This will help distribute oil inside of the door closer body.

5. Once the oil is full put the door closer end cap back on the closer body. Unscrew the "S" valve so that it is almost all the way out. Do not unscrew it all the way, as we do not want oil to leak out. Slowly screw in the door closer end cap this will allow the air to bleed out of the "S" valve. Air bubble will gurgle out of the "S" valve. Once air is no longer visibly bleeding out of the valve, screw in or close the valve to the normal position and fully tighten the door closer end cap.

Repair Vs Replacement Pros and Cons

Availability Of Parts

The biggest concern of whether to repair or replace a door closer is cost. In the early 1960's under floor door closers were very popular. Floor closers were large closer bodies that were cemented into the floor underneath the door. Due to the door closers being cemented into the floor, replacement was often tedious and difficult, requiring concrete to be broken and new concrete required for the replacement door closer. For this reason door closers were repaired and rebuilt as an alternative to a new replacement. However, during these times manufacturers often offered rebuild kits which included the exact O-Rings, seals, and bearings needed to properly repair the door closer. In today's market, floor closers are rarely used. Instead commercial overhead surface mounted door closers are the standard. These door closers vary in size and components. As an example, today there are hundreds of different door closer brands, each brand with a slightly different model and design. Meaning one door closer's O-Ring is different than another door closer manufacturer's O-Ring. For this reason door closers today are simply replaced since specific parts are not available from most manufacturers.

Sourcing Parts

With parts unavailable for door closers, it makes it difficult to repair. Seals and O-Rings can be sourced, but then the problem is quantity. Most companies who sell O-Rings and Seals typically sell them in large packs. When somebody only needs 1 O-Ring seal, it may prove difficult to find a vendor that will sell you just one.

Special Tools

Having the parts is one thing, but being able to remove a door closer end cap is another. Most door closer end caps require a special wrench for removal. These wrenches are not available at any store and most are custom made. Creating this special door closer wrench can take alot of time.

Hydraulic Fluid

Hydraulic fluid can be expensive, atleast if you are using the correct stuff for door closers. A commercial door closer uses a special hydraulic fluid blend with specific viscosity parameters and properties so that it can operate in commercial environments.


It takes time to find all of these specialized parts, create the tool to work on the door closer, and then replace and install the parts.

Many people assume repair is always the most inexpensive choice, however when it comes to door closers today, this is just not the case. Taking into account all these factors, replacing a defective door closer with a new door closer is always the best choice. New door closer replacement is made easy. In our article on "How To Replace A Door Closer" we go over how to get an exact door closer replacement that will bolt into your old door closer mounting holes, making installation fast and easy. So if the door closer is leaking, don't bother attempting to repair it, just replace it!


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