Piston or spring? How a murphy bed mechanism actually works

Every murphy bed is a cabinet, a frame that holds the mattress, and a mechanism that makes a hundred pounds feel like ten. The mechanism is the part you touch every day and the part that fails first when it is wrong. Here is how the two kinds work, how they are tuned, and what to look for in a murphy bed kit if you are building the cabinet yourself.

The two kinds

Piston (gas strut). Two or four gas cylinders, the same idea as the struts that hold up a car hatch, mounted between the cabinet and the bed frame. They push the frame toward closed. With the mattress on, the weight of the bed and the push of the pistons nearly cancel, so the bed floats down and lifts back with a light pull. Pistons are the default on almost every bed built in Utah today, and on ours.

Spring. A set of coil springs on each side under tension, hooked to a pivot at the base of the cabinet. Pull the bed down and the springs stretch; lift and they pull it home. Springs have been in murphy beds for a century and they still work. They are also louder, need more adjustment, and need a stronger cabinet to carry the load at the pivot.

Tuned to the mattress

Neither mechanism knows what mattress you own. A piston is rated for a load. The bed maker picks the piston count and pressure for the mattress weight and bed size you tell them, which is why every order asks about the mattress, not just the size. Put a heavy hybrid on a bed tuned for a light foam mattress and it drops too fast and fights you on the way up. Put a light mattress on a bed tuned heavy and the bed will not stay down without the legs.

Springs tune by adding or removing springs and by moving the hook position. That is the DIY appeal: you can adjust it yourself with pliers. It is also the DIY problem, because you will.

Mattress thickness tops out around 11 or 12 inches on both kinds, no box spring. Very heavy mattresses, a king latex or a thick hybrid, are the case where a spring mechanism still gets specified, because the spring count can go higher than the piston rating.

What lifts with one hand

A correctly tuned piston bed. A kid can bring a queen down and a grandparent can put it back up. The legs fold out as the bed comes down and the last few inches are slow. A spring bed lifts with one hand when it is tuned well and the mattress has not changed. Change the mattress, add a topper, and it needs two hands and a shoulder until someone re-hooks the springs.

Safety: legs, straps, release lock

• Legs. Folding legs at the foot take the weight when the bed is down. They are not optional. A bed down on its mechanism alone is stressing the pivots.
• Straps. An elastic strap or two across the mattress keeps the bedding on when the bed goes up. Without them the pillows end up on the cabinet floor and the doors do not close.
• Release lock. A latch at the top of the frame holds the bed closed, with a lock for homes that have small kids. A piston bed pushes itself closed, so the latch is a backup there. On a spring bed the latch does the holding.
• Anchoring. Vertical beds anchor to the wall at the top of the cabinet. This is what keeps a cabinet with a mattress in it from tipping while the bed is moving. Cabinet chest beds skip it because they are low.

What wears out

Gas pistons lose pressure over years, the way a car hatch eventually starts to sag. The sign is a bed that gets heavier to lift. Pistons are a bolt-off part, and a replacement set is a short job. Springs stretch and lose tension slowly and the hooks wear. Spring beds also squeak, and the noise tends to come back after you lubricate it. On either kind the pivot bolts should be checked once a year and the legs tightened.

Murphy bed hardware kits and DIY

A murphy bed kit from a hardware supplier is the mechanism, pivots, legs and plans. You build the cabinet from plywood or sheet goods to their drawings. Piston kits ship with a piston specified for a mattress weight range. Spring kits ship with a bag of springs and a tuning chart.

Most people who build one regret choosing the spring kit. The springs are tuned by trial, the cabinet needs to be heavier and more rigid at the base to take the pivot load, and the bed never feels like the one in the store. A piston kit is more forgiving: get the mattress weight right, build the cabinet square, and it works the first time. See kit vs custom for what the build actually involves and installation for the anchoring.

Send a photo of the wall and tell us what mattress you plan to use. We reply the same business day with the mechanism we would spec and why.