Elevator Maintenance Audit Hydraulic Fluid Temperatures


Is your hydraulic elevator Installed Correctly and Maintained Correctly? These sound like they are blunt questions. However, you would be shocked how many hydraulic elevators are not installed correctly and are not maintained correctly. Let’s look at just one aspect of the hydraulic elevator and you should be aware of.

Viciedo Consulting highly recommends that your hydraulic elevator fluid be maintained at a temperature of 100°F ± 10%. Why: A) Inevitable change in fluid viscosity due to change in fluid temperature B) The possible breakdown of the fluid at high temperatures.

We will not go into details as to the specifics on Hydraulic elevator pumps and valves. In short, the hydraulic elevator utilizes a positive displacement pump to compress hydraulic fluid into the system and force the elevator to move upward. In the downward direction, the pump is not activated. Gravity brings the elevator downward and the elevator’s valve controls that decent by accurately metering the amount of fluid that can flow from the system back into the hydraulic reservoir. All this mechanical and electrical activity generates a tremendous amount of heat via friction and conduction. The hydraulic fluid by both design and inadvertently, retains a great deal of this heat and is required to dissipate it to a certain extent. Hence, the issues arise.

As fluid viscosity changes, the rate of flow the fluid may achieve through the valving changes. Therefore, the elevator’s performance may change. Yes, hydraulic valves are temperature compensated but only to a limited extent. When the delta in fluid temperatures is too great, the valving simply cannot compensate properly.

Was your hydraulic elevator properly installed and is it properly maintained? We can start by asking which hydraulic fluid is currently in the system? Did your Elevator Consultant specify and confirm that a hydraulic fluid with a viscosity index greater than 100 is utilized in your system? The reason is simple; the higher the viscosity index, the less change in viscosity with temperature. With the right fluid, your hydraulic valve can adequately compensate and adjust the elevator’s performance as needed.

As a rule, when we see hydraulic fluid temperatures running in excess of 100°F, your elevator requires a heat exchanger (Oil Cooler) in order to maintain the hydraulic fluid at proper operating temperatures. The necessity for a heat exchanger adds another issue to the equation; machine room environmental control. All too often, we can displace unwanted heat from the elevator’s hydraulic and control system. However, the heat is displaced into the elevator machine rom and the room’s environmental control is incapable if displacing the heat creating an unwanted vicious circle, for lack of better words.

Now the bad part. Oxidization of hydraulic fluid normally begins at temperatures above 167°F. Sadly, the rate of oxidization nearly doubles for every 50°F above that. It goes without saying that degradation of the hydraulic fluid can lead to extremely costly repairs and/or damage.

All too often, when you “smell” hydraulic fluid from within the elevator cab or the machine room, fluid degradation has already begun because what you are smelling is the fluid breaking down. Normal hydraulic fluid is not odorless by any means. But you cannot smell it in the cab and the machine room does not carry an overwhelming scent of it either.

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The hydraulic elevator is quite efficient in the up direction with an overall efficiency in the order of 90%. In the down direction, however, the efficiency is zero; all of the potential energy being converted to heat in the fluid.

Ironically, the vast majority of “elevator experts” believe that the hydraulic elevator crates the majority of its “heat” in and around the hydraulic fluid do to the UP runs when the motor and pump are forcing oil into the system. Simply put, if we use a typical hydraulic elevator with a 30 hp motor running at 100 fpm with a 2500# capacity, we would recognize an approximate 10% loss in the UP direction and a 90% loss in the DOWN direction. Running the elevator UP 3-floors the calculation would be approximately, 20 secs running up (0.1*30 hp) and 20 seconds down (0.9*30 hp) resulting in approximately 12.4 Wh UP and 112 Wh DOWN. Therefore, each trip would generate 424 BTU.

We can see that the original elevator specification and installation may have a profound impact as to whether our elevator is running and performing properly. Additionally, if our maintenance is not adequate and a cheaper hydraulic fluid was added to our system, we may have issues also.

The summary is, who is your Trusted Advisor? The elevator in your building is one of the riskiest assets you will own. You need a Trusted Advisor who is looking out for your interest, and only your interest. Viciedo Consulting is that experienced and knowledgeable Elevator and Escalator Consulting Firm who always places your Risk Mitigation needs in the forefront. We understand the litigious nature of the Elevator Industry because we specialize in Elevator Litigation Consulting. Call us to see how we can be your Trusted Advisor.

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