Hydraulic Elevators Basic Components

In the following previous Topics:

• Basic Elevator Components - Part One
• Basic Elevator Components - Part Two
• Elevator Machine and Drive System
• Elevator Safety System
• Elevator Control System – Part One
• Elevator Control System - Part Two

I explained all the basic components for the traction elevators (Pull elevators) and today I will explain the basic components of the Hydraulic Elevators (Push Elevators) as follows.

You can review the following previous topics for more information and good following.

• Elevators Types and Classifications  – Part One
• Elevators Types and Classification - Part Two

Hydraulic Elevators (Push Elevators) types:

Hydraulic Elevators (Push Elevators) types

Hydraulic elevators are supported by a piston at the bottom of the elevator that pushes the elevator up. They are used for low-rise applications of 2-8 stories and travel at a maximum speed of 200 feet per minute. The machine room for hydraulic elevators is located at the lowest level adjacent to the elevator shaft.

Hydraulic Elevators Types

Hydraulic Elevators Types

Hydraulic elevators have many two main types as follows:

A- Holed (Conventional) Hydraulic Elevators

They have a sheave that extends below the floor of the elevator pit, which accepts the retracting piston as the elevator descends. Some configurations have a telescoping piston that collapses and requires a shallower hole below the pit. Max travel distance is approximately 60 feet.

B- Hole-less Hydraulic Elevators

They have a piston on either side of the cab. It can be divided to 3 different types as follows:

a- Telescopic Hydraulic Elevators:

In this configuration, the telescoping pistons are fixed at the base of the pit and do not require a sheave or hole below the pit and has 2 or 3 pieces of telescoping pistons. Telescoping pistons allow up to 50 feet of travel distance.

b- Non-telescoping (single stage) Hydraulic Elevators:

It has one piston and only allows about 20 feet of travel distance.

c- Roped Hydraulic Elevators:
They use a combination of ropes and a piston to move the elevator. Maximum travel distance is about 60 feet.


Hydraulic Elevators components:

Hydraulic Elevators components

The Hydraulic Elevators will differ from the traction elevator in the following main components:

1. Machine/drive system.
2. Safety system.

1- Machine / Drive system:

The lift car shall be driven by one of the following methods:

1. Direct acting.
2. Indirect acting (suspended) hydraulic system in case of using Roped Hydraulic elevator. 

In case of direct acting system, the hydraulic ram shall be located either at the side, or the back. Unless otherwise specified, direct acting underneath the lift car is not acceptable.



The machine/ drive system will include the following components:

1.A plunger/piston/jack
The cylinder shall be constructed of steel pipe of a sufficient thickness and suitable safety margin. The top of the cylinder shall be equipped with a cylinder head with an internal guide ring and self-adjusting packing.

The plunger/Ram shall be constructed of a steel shaft of a proper diameter machined true and smooth. The plunger shall be provided with a stop electrically welded to the bottom to prevent the plunger from leaving the cylinder.


1.B Hydraulic power unit 

Hydraulic power unit 

The power unit shall be generously rated and shall operate with minimum noise and vibration. The unit shall be mounted on vibration insulators above the machine room floor. A silencer unit shall be fitted in the hydraulic system to minimize the transmission of pulsations from the pump to the car and the elimination of airborne noise.

The hydraulic power unit consists of the following components:

1. The Tank.
2. Motor/Pump.
3. Valve.
4. Actuator.

1.B.1 The Tank 

The Tank

The tank shall have sufficient capacity to provide an adequate reserve to prevent the entrance of air or other gas into the system. A sight glass tube shall be provided for checking the oil level and the minimum level mark shall be clearly indicated. An oil level monitoring device shall be provided, and if operated, shall maintain a visual and audible signal in the control panel until the fault is rectified.

So, the main function of the tank is holding the liquid used in the system, This liquid is usually oil based because:

• Non compressible.
• Self lubricating.

1.B.2 Motor/Pump
The main function of the pump used in hydraulic elevator is constantly pushing Liquid into the cylinder to lift the elevator, the pump is Submersible type with Variable Speed Valve Leveling.

The pump and pump motor shall be mounted on one robust bedplate or within the power unit assembly if it is suitably rigid. The motor pump and bearing(s) shall be so mounted and assembled that proper alignment of these parts is maintained under all normal operating conditions.

An oil filter shall be fitted on the pump inlet. A stopcock shall be provided to enable the filter to be cleaned or changed without significant loss of oil. The pump motor shall be of the single speed squirrel cage or slip ring type and it shall run with minimum noise and vibration.



1.B.3 Valve
The power unit control valve shall be a variable speed proportional valve type that includes all hydraulic control valving inherently. A stopcock shall be provided between the control valves and the cylinder(s), and also between the reservoir tank and the pump if the pump is mounted outside the tank.

The main functions of the Valve are:

• Lets Liquid out of the system. 
• Keeps the pressure low when open.
• Increases pressure when closed.

This valve shall incorporate the following features:

• Up and down acceleration and deceleration speed adjustment for smooth starts and stops. 
• Smooth stops at each landing shall be an inherent feature of the valve. 
• Adjustable pressure relief valve. 
• Manually operating 'DOWN' valve to lower elevator in an emergency. 
• Pressure gauge indicating in P.S.I. and Bars. 
• Gate valve to isolate cylinder from pump unit. 
• Negative pressure switch. 

1.B.4 Actuator
An actuator is the device that transfers fluid or electrical energy into mechanical energy.

The actuator could be piston because it moves up and down.

Note: In very old installations, a car is raised or lowered by a ram powered by water pressure. Newer installations use oil pressure to power a ram. Some less modern hydraulic elevators and hydraulic elevators that travel over six stories may use cables and counterweights.


1.C Suspended system (in case of using Roped Hydraulic elevator)

Suspended system

• The car cage is suspended from a wire cable, and a jigger consisting of a fixed cylinder, a sliding ram, and a set of two pulley blocks, which is provided at the foot of the hole of the cage. One pulley block is movable while the other one is fixed. The sliding ram end is connected to the movable pulley block. The cage is suspended from the other end of the rope. The raising or lowering of the cage of the lift is done by the jigger. This arrangement is used to increase the speed of the lift by a 2:1 roping ratio. Car speed up to 150 feet per minute is attained and maximum travel length is 48 feet (14m). 

• Where the car is suspended, the cylinders shall be solidly mounted on the building structure and the head of the ram adequately guided or supported to carry the rope pulley. A device shall be incorporated which will initiate the closing of the lowering valve in the event of the car being prevented from descending by an obstruction. The device may be either a low pressure switch in the hydraulic line or a slack rope switch. 

2- Safety System 

The hydraulic elevator has dominated the low-rise market because it is cheaper to build, install and service, and because it has a decidedly better safety record than the electric elevator. Especially in earthquake endangered areas, the hydraulic elevator has proven itself to be clearly the safer option. Due to the threat presented by swinging counterweights and also because the car is suspended from the top of the hoistway, the traction elevator is particularly vulnerable to a shaking building compared to the hydraulic elevator which is installed practically on the building’s foundation.

The safety system will include the following components:

2.A Manual reset slack rope safety switch
A "slack/broken cable" safety device shall be supplied which will stop and sustain the elevator and its rated load, if either of the hoisting cables become slack or breaks. The safety device shall be resettable by the operation of the elevator in the upward direction. A switch shall be mounted in such a position as to sense the operation of the safety device, and will open the safety circuit to the controller to prevent operation of the elevator in either direction.

2.B Final Limit Switch
The elevator shall be equipped with a final limit switch to cut off all power to the elevator if the upper normal terminal stopping devices fail.

2.C Seismic valve for hydraulic elevators 

Seismic valve for hydraulic elevators

A valve located in the pit close to the jack that is designed to hold pressure if the hydraulic line is broken due to seismic activity.

2.D Buffers
The buffer-striking member on the underside of the car must stop the elevator before the jack plunger reaches its down limit of travel.

2.E Anti-creep device
Provision shall be made to automatically return the car to the landing level at a speed not exceeding 0.15 m/s in the event of a leakage in the hydraulic system causing the car to move downward for more than 75 mm but within the unlocking zone.


2.F Manual emergency operation
Readily accessible manual devices for emergency operation shall be provided in the machine room.


2.G Other Safety Devices

• Automatic bi-directional leveling.
• Pit switch.
• Pump run timer.
• Car top stop switch.
• Emergency battery back-up for lighting, alarm and lowering.
• Cab gate safety switch.

Method of operation for Hydraulic Elevators

Method of operation for Hydraulic Elevators

1- For Direct Acting Type

• The pump forces fluid from the tank into a pipe leading to the cylinder. When the valve is opened, the pressurized fluid will take the path of least resistance and return to the fluid reservoir. But when the valve is closed, the pressurized fluid has nowhere to go except into the cylinder. As the fluid collects in the cylinder, it pushes the piston up, lifting the elevator car. 

• When the car approaches the correct floor, the control system sends a signal to the electric motor to gradually shut off the pump. With the pump off, there is no more fluid flowing into the cylinder, but the fluid that is already in the cylinder cannot escape (it can't flow backward through the pump, and the valve is still closed). The piston rests on the fluid, and the car stays where it is. 

• To lower the car, the elevator control system sends a signal to the valve. The valve is operated electrically by a basic solenoid switch (Actuator). When the solenoid opens the valve, the fluid that has collected in the cylinder can flow out into the fluid reservoir. The weight of the car and the cargo pushes down on the piston, which drives the fluid into the reservoir. The car gradually descends. To stop the car at a lower floor, the control system closes the valve again. 

2- For Indirect Acting (Suspended) Hydraulic System Type 

• Water or any hydraulic fluid at a high pressure is admitted into the fixed cylinder of the jigger. This high pressure hydraulic fluid pushes the sliding ram to move towards left side as shown in the figure. When the sliding ram moves towards the left side, the distance between the fixed and movable pulleys increases and thus the cage is lifted up.

• When the water or the hydraulic fluid under high pressure inside the cylinder is released, then the distance between the two pulleys decreases and thus the cage comes down. Thus the suspended-type hydraulic lifts are more popular than direct type lifts. 

Hydraulic Elevators Machine Room

Hydraulic Elevators Machine Room

The equipment rooms for hydraulic elevators are normally located at the lower level of a building, but can be at any floor level or 50 to 100 feet away from the elevator shaft.



Machine Room Electromechanical Requirements

Machine Room Electromechanical Requirements

• The hydraulic pump unit, GFI duplex receptacle and fused disconnect switches (elevator lighting) must be located in a dedicated machine room. 

• Adequate working space in the machine room includes clearance in front of the pump unit and the proper location of the light switch and disconnect switches. 

• Two dedicated PVC sleeves, at least 3” (76 mm) in diameter, will be required between the hoistway and the machine room, one sleeve for the hydraulic hose and one for the electrical conduit. This is to enable the installers to make the connection between the cylinder and the pumping unit. The sleeves should enter the hoistway at either corner of the support wall. 

• The machine room must be provided with at least 100 lx lighting over the pumping unit and disconnect switches. 

• The machine room must be provided with two lockable fused disconnects rated for the pumping unit. Disconnect switches should be located on the strike (lock) side of the machine room door. 

• At least one GFCI duplex receptacle connected to a 15 amp branch circuit shall be installed in the machine room. 

This Topic will be the last one that explains the Traction elevator components and In the next Topic, I will explain the Escalators Basic Components . So, please keep following.


Note: these topics about elevators in this course EE-1: Beginner's electrical design course is an introduction only for beginners to know general basic information about elevators as a type of Power loads. But in other levels of our electrical design courses, we will show and explain in detail the Elevator Loads Estimation calculations.