SUBJECT : The sealing of hot oil 3-5

The largest user of hot oil pumps is the heat transfer oil customer. Many consumers use these products with oil temperatures exceeding 500° Fahrenheit (260° C.) and 600° to 700° F. ( 315° to 370° C.) becoming common. Some hotels have recently installed these systems in their laundry to dry clothing.

Heat transfer oils have many advantages over the steam that was formally used in these applications.

In addition to these heat transfer oils, you'll encounter hot petroleum oil applications in refineries and hot organic oil applications in various other industries. There are several problems associated with sealing these hot oil products and each of them has to be solved if satisfactory seal life is ever to be obtained.

Although there are many techniques available to the seal man to address each of these problems, the combination of these problems eliminates most of the common techniques and leaves the customer with very few options to get good seal life. Regardless of the seal selected you must address all of the problems or the seal life will be shortened.

Oil refineries pump hot oil with closed impeller pumps and, as a result, have to put up with the additional problems associated with replacing "closed impeller" wear rings. Unlike the chemical industry they cannot take advantage of the features of an open impeller design that can be easily adjusted to maintain maximum efficiency. There are two reasons why oil refineries chose closed impeller designs with mechanical seals and A.P.I. glands :

To insure long seal life you must do the following:

The product has to be cooled in the seal chamber :

You must install a back up seal for the following reasons:

A large diameter cooled sealing chamber should be installed on the pump.

A Cartridge seal is necessary.

To compensate for misalignment you will have to :

The illustration shows the centerline design. It will allow the pump volute to thermally expand both up and down, and thereby eliminate strain on the suction piping.

Now that we have discussed these important points lets take a look at some solutions that are often offered, but that we should not adopt as our solution. Here are the things that do not work well :

Bad solution #1. Use a metal bellows seal to eliminate the need for cooling in the seal area.

Comment: Although the metal bellows doesn't have rubber parts that are sensitive to high temperature cooling is still needed for the coking. Most bellow suppliers offer an A.P.I. type gland to provide low pressure steam behind the seal for cooling purposes and thereby eliminate the option of backup sealing. This quenching should be limited to only a back up cooling status. If quenching is done with water rather than steam, watch out for a calcium build up outboard of the seal. This "hard water" build up can restrict the movement of the flexing portion of the seal as it tries to compensate for face wear.

If you substitute condensate for the quenching fluid the build up can be eliminated almost entirely.

Bad solution #2. Run a line from the discharge of the pump through a cooler and filter to cool down and clean up the oil going into the stuffing box.

Bad solution #3. Use two seals and run a cool oil between them.

What then is the best solution that addresses all of the problems? Look at the following illustration:

That's all there is to the application. Centrifugal force will clean up the small amount of fluid in the sealing chamber while the cooling jacket holds the temperature low enough to prevent coking and injuring the seal elastomer.

The only problem with this system is that it works so well we often forget to clean the cooling jacket on the pump. A small layer of calcium inside this jacket will provide an insulation and destroy the cooling affect of the jacket. Be sure to keep this jacket clean or substitute steam or condensate for the cooling water, and then don't worry about it.

Here are a few additional thoughts:

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