Fire Water Pump Gear Box Overheating 1

[thkurian]

When engine driven vertical turbine type fire water pup is shop tested, right angle gear box temperature is found to be 62 deg above ambient for radial bearing and 42 deg above ambient for thrust bearing. Pump is 5000 gpm capacity with head of 132 m. Same temperature is found in similar 4 pumps. Gear box sizing is checked and found meeting power rating, downthrust and speed. What can be the causes? which one is likely to be faulty - gear box or pump?

 

[LittleInch]

Are they faulty?? If 4 of them are doing it maybe that's the normal operating temperature?

Is there supposed to be oil circulation or other gearbox cooling??

I get the power to be approx. 600kW so if even a very small percent is released as heat in the G Box it will heat up qite a lot.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

Whatmakes you think anything is faulty?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[JJPellin]

Are you running the engine at the correct speed? Are you using the correct oil as recommended by the gearbox manufacturer? Are you providing cooling as specified by the gearbox manufacturer? We have six engine driven pumps of the type you describe. All of ours have internal or external coolers for the gearbox oil. I assume the temperatures you provide are in °F. 40 to 60 °F above ambient seems just fine to me.

Johnny Pellin

 

[thkurian]

As per API 610, 11th Edition, Clause 6.10.2.4b - For ring oil or splash system, oil sunp temperature below 82 Deg C (180 Deg F). During shop testing, the pump oil temperature shall not exceed 40K (70 Deg R) and (if bearing temperature sensors are supplied) outer ring temperature shall not exceed 93 Deg C (200 Deg F).
The gear box is provided with cooling coils, water taken from fire water pump discharge. The shop test site ambient temperature is 20 DegC. The actual site maximum temperature is 50 Deg C.

The temperature rise observed during tests is 62 and 42 Deg C. These are above permitted temperature rise of API 610. At site, actual temperature can go as high as 112 Deg C.

The gear box is using spherical roller thrust bearings which requires a minimum downthrust to operate. If pump impeller bottom touches casing, downthrust will be taken by casing and spherical roller bearing will operate without downthrust and can cause hearing heating and failure.

The engine speed is 1825 rpm, for gear box maximum input speed is 3520 rpm. Hence speed is OK. Maximum absorbed power is 615 kW. Engine power rating is 738 kW at 1825 rpm, Gear box rating is 695kW at same speed. Hence power rating is OK.

 

[Artisi]

What does API 610 have to do with fire pump acceptance? Spherical roller bearings can run a bit on the warm side on initial start up but seem to settle down after a run-in period.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[thkurian]

API 610 is followed for pump design and construction. For performance selection, NFPA 20 is followed. Is bearing oil temperature as high as 112 Deg C accepable at site conditions. API 610 allows maximum 93 Deg C. Gearbox manufacturer recommends mineral oil for temperature upto 82 Deg C and synthetic oil for themperature above 82 Deg C. However the fear is about the failure of bearings due the excessive heating.

 

[ccfowler]

I would check carefully to verify the suitability of the lubricants in use. It is not unusual for excessive oil viscosity to be a significant factor in excessive temperature problems.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[Artisi]

thkurian: has the temp. rise / acceptability / rejection been discussed with the gearbox manufacturer - always a good place to start.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[thkurian]

This issue was discussed with Gear Box manufacturer and their recommendation is to use mineral oil with change in every 3 months and synthetic oil with change in every 6 months. The cooling water flow is 42 lpm. One factor they might be missing is functioning of thrust bearing of gear box which takes downthrust of pump also. They might not be looking in this matter.

 

[Artisi]

I would assume as a gearbox manufacturer they would be fully aware of the imposed loads on the bearings.
Edited to add: Have you involved the bearing manufacturer with your concerns?
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[thkurian]

Gear Box Vendor is the sub Vendor of Pump Vendor. Hence we do not have direct contact with Gear Box Manufacturer. Gear box was selected for the downthrust provided by Vendor. My point is if downthrust disappears due to contact between impeller and casing at bottom (due to shaft extension during operation of pump), spherical roller bearing is going to be heated up.

 

[Artisi]

And if a meteor hits the pump station it could will undoubtedly cause some damage.

Why will the impeller hit the pump casing if the impeller is set correctly during installation, seems I missed this secondary question along the way as you started out talking about temp. rise of the bearings during test.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[JJPellin]

In my experience, issues during testing of fire water pumps can result from the testing requirements. If the cooling water comes off the pump discharge inside the control valve, there may be inadequate flow when testing at run-out (end of curve). If the cooling water comes off after the control valve, there may be inadequate flow when testing at zero flow. The pump thrust can vary drastically over the test flow range. There may be up-thrust when testing at high flow. There may be high downward thrust when testing at low flow.

Johnny Pellin

 

[thkurian]

Thanks for al the input. Will inform the final findings once Vendor comes out with any suggestions (like increase of setting height, increase of cooling water flow, reduction of engine and pump speed) and implementation to reduce the temperature within a rise of 40 Deg C above ambient. Right now gear box is not accepted.

Cooling water outlet is on fire water pump discharge elbw.

 

[thkurian]

It was observed that pump Vendor had installed an orifice in the cooling water line to gear box cooler of very small diameter which can flow only 1/4th of designed flow. The orifice diameter is increased to more than double which as per calculations can provide the required flow. The testing is moved to site when the pump undergoes commissioning.