Fluke 720A KVD oil seal - Page 1
Forum section: electronics / general

author: texaspyro
author_rank: Super Contributor
timestamp: October 01, 2017, 04:47:14 pm
content: My 720A developed a small leak at the resistor can oil seal. The seal does not seem to be in the manual, so I contacted Fluke. They seemed a bit baffled about what it could be. I sent them a couple of photos and they finally came up with:171959 EA 23.70Item Desc :SEAL,BUNA,3/8 EXT THREAD,COMPOSITE,STEEL RETAINER,CADMIUM PL,.750 OD,.063 THKSo, only 24 bucks for a 50 cent bolt and 10 cent O-ring.I don't think enough oil leaked to make a difference, but I also asked them about what oil to use and they responded that they don't sell the oil, but to use "Grade 5 mineral oil"... I assume that is viscosity 5. Does anybody know of a suitable oil available in small quantities? I'd prefer not to go dumping in some no-name goop of unknown quality/purity/virginity from the local hardware/grocery/etc store.

author: MK
author_rank: Regular Contributor
timestamp: October 01, 2017, 04:57:13 pm
content: two choices, vacuum pump oil or medicinal parafin are suitable alternatives, some mineral pump oil is straight parafin to cope with oxidisers in the vacuum stream, a choice of viscosities available there too.

author: SeanB
author_rank: Super Contributor
timestamp: October 01, 2017, 05:07:27 pm
content: Buna rubber, so I would go with a vacuum pump oil. Simply remove 10ml of the existing oil and place in a glass jar, and introduce 10ml of your intended oil to it as well, and seal the jar and leave for a few days to see if there is any interaction, which will show as either separation of the oils or one turning to gel. otherwise mineral refrigerant oil ( which I use as vacuum pump oil, make sure it is mineral and not POE or even worse PAG which is conductive) will also work, or just go to the hardware and get transformer oil.All the oils of course will need to be vacuum dewatered and degassed before use, preferably also heated to 70C as well during this, to get them as dry as possible so you do not introduce any moisture into the sealed system.

author: texaspyro
author_rank: Super Contributor
timestamp: October 02, 2017, 12:30:05 am
content: It looks like most vacuum pump oils are rather viscous. I am assuming when Fluke said "Grade 5" mineral oil that they meant 5 weight (rather thin). What leaked out (maybe a tablespoon) was thin (like baby oil).I don't think enough leaked to matter, but I dont know about the earlier history of the machine. This is what Fluke said:"The oil is a grade 5 mineral oil: we don’t get it in small quantities he has to get it from somewhere where it is sold in a quart or small quantities. Why does he need to change the oil? And has he lost a lot of the oil He does not need to have it completely full. If it is visible where it is up to the internal PCB in the can that is more than sufficient. As when he ships it or sends somewhere when it is on a plane the pressurization will cause it to leak if it is too full."I have not tried looking into the can. The way it is mounted may require some disassembly to see into the hole.

author: floobydust
author_rank: Super Contributor
timestamp: October 02, 2017, 03:56:04 am
content: I've had products with o-ring seals leaking and given MecE's an earful about it.Thermal expansion of the oil and can, and seal-interface, altitude/barometric pressure differences were found to be the causes. Mostly o-ring compression was not enough.Now I understand why car headlight fixtures use Gore-tex vents instead of trying to absolutely seal them.I would replace the o-ring possibly AS568-016, local o-ring shop charges $1 for a bunch.Not sure if mineral oil stays homogeneous after years or the lighter distillates rise up. The thin oils might have seeped out.

author: texaspyro
author_rank: Super Contributor
timestamp: October 02, 2017, 04:19:40 am
content: When it started leaking a few years ago, I replaced the o-ring with one I had... the Fluke people noticed that when I sent them the photo. I wasn't convinced that was good enough, so I have been keeping the chassis vertical to make sure it didn't have a way to leak. Recently, I decided I needed to fix it properly...There is a sticker in the machine that says to tighten the bolt finger tight, then an additional quarter (?) turn.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 02, 2017, 07:29:32 am
content: Instructions like finger tight + 1/4 turn are rather common for screws with seals. This is a way to ensure a reasonable reproducible compression on the seal. Too much compression can damage the seal, especially if in contact with oil.

author: floobydust
author_rank: Super Contributor
timestamp: October 02, 2017, 06:10:01 pm
content: It leaked, you replaced the o-ring, later it leaked again- is that right.You might have a rough surface or burr on the screw or lip, which can damage the o-ring during tightening (you can look at both with a magnifier or microscope).I think the same if it's dry- the o-ring gets abrasion or stretched so some lube (mineral oil) must be present on the o-ring for installation.Parker O-ring handbook 292pgsis very detailed and goes in deeper than imaginable.

author: texaspyro
author_rank: Super Contributor
timestamp: October 02, 2017, 10:29:06 pm
content: No, at the time I was using it for some tests and I kept the unit vertical on the side and never gave it a chance to leak again. Recently, I got tired of seeing it standing on its side and decided to fix it properly.I'm rather familiar with o-rings. All my rocket motors use O-rings to seal 1000+ PSI gases in a 5000 degrees F environment.

author: dacman
author_rank: Frequent Contributor
timestamp: October 03, 2017, 04:10:32 am
content: Hart Scientific, which is now Fluke, sells Drakeol 7 mineral oil.http://us.flukecal.com/literature/sds-safety-data-sheets/fluke-5011-mineral-oil-drakeol-7-white-mineral-oilhttp://us.flukecal.com/products/temperature-calibration/calibration-baths/bath-fluids/calibration-bath-fluids?quicktabs_product_details=3

author: branadic
author_rank: Super Contributor
timestamp: October 03, 2017, 07:29:27 am
content: In conctact with mineral oil not every sealing material is appropriate. Please make sure you have the correct sealing material, that can resist mineral oil. You want to use a sealing made of fluor rubber (Viton) for yor purpose.-branadic-

author: texaspyro
author_rank: Super Contributor
timestamp: October 03, 2017, 04:08:31 pm
content: Quote from: branadic on October 03, 2017, 07:29:27 amFluke specifies that the seal gasket is Buna...

author: texaspyro
author_rank: Super Contributor
timestamp: October 04, 2017, 07:53:55 pm
content: Quote from: dacman on October 03, 2017, 04:10:32 amI asked Fluke if that oil would be suitable and the answer was a resounding... "I dunno".Nobody seems to know what Fluke means by "Grade 5 mineral oil"... including the mineral oil manufacturers I have asked.

author: Gyro
author_rank: Super Contributor
timestamp: October 04, 2017, 08:31:37 pm
content: From the sound of it, you've lost virtually no oil. A tiny amount of oil can look like a lot when it wets the surface of a panel.If it didn't get to the drips stage then I suspect that you are far more likely to do damage by mixing oils, introducing moisture etc. than you are by just re-sealing it. Having a small dry air bubble sounds far less risky.I doubt if the chamber was filled right to the screw threads anyway - Maybe it was but that sounds messy in production, especially when they were trying to avoid contamination of everything else.

author: floobydust
author_rank: Super Contributor
timestamp: October 04, 2017, 09:16:34 pm
content: Surely you need some air for expansion, I can't see filling it right up.Mineral Oil, light (paraffin oil, light), #5Synonyms: Drakeol (R) 7; White Mineral Oil; Mineral Oil, light, white; Paraffin oil; NujolCAS Number: 8042-47-5TheDrakeol 7is cosmetic grade, used in food packaging - coating fruit and vegetables.You could do a sample request.

author: texaspyro
author_rank: Super Contributor
timestamp: October 04, 2017, 10:22:05 pm
content: Quote from: Gyro on October 04, 2017, 08:31:37 pmI don't think I lost much oil, but don't know for sure. It's rather hard to tell how much has gone bye-bye due to the way the can/seal is mounted. I was made an offer I couldn't refuse for my flexible, tiny borescope a long time ago.I'm just checking for what to use if I do need some. Plus, it would be nice to have some for a couple of projects and if it's good enough for a 720A, it's good enough for whatever.

author: dacman
author_rank: Frequent Contributor
timestamp: October 05, 2017, 11:30:23 pm
content: I had a 720A that leaked for maybe a year (when set on its side for storage). When I took the oil plug bolt out to check how much was left, I couldn't tell that there was any missing. It seemed full. I was in near disbelief.Fluke gets over five times the price of mineral oil on Amazon for their 5011 mineral oil (for a gallon). One use for it is oil baths with standard resistors, (which is how it's been used for years at my day job).

author: CalMachine
author_rank: Frequent Contributor
timestamp: October 11, 2017, 12:04:02 am
content: Quote from: dacman on October 05, 2017, 11:30:23 pmI've recently picked up a ~15 gallons (56 liters) of Draekol 7 and WO-10 for our Oil bath. Ihighlysuggest shopping around. Fluke waswellover 5x the price I got this stuff for.

author: Edwin G. Pettis
author_rank: Frequent Contributor
timestamp: October 12, 2017, 03:34:19 pm
content: The mineral oil I've used is from STE Oil Company, Inc., crystal plus oil 200PS, a heavy mineral oil, food grade. Shipping cost more than the gallon of oil the last time I bought it. How long the oil lasts depends on how it is used, if it is in an open container, it tends to get dirty from air contamination so you might end up with only 6 months to a year life. If it is in an enclosed container, like a resistor standard, the oil will last for years. However it will slowly degrade and that is the main reason for having to replace it. Under normal enclosed conditions, it can last more than ten years. The color tends to change and become a bit darker over the years. I usually just change it out about every decade since it isn't too expensive.