Vacuum hose length requirements

[IdiotFool]

Good morning, all.

I have a Shimadzu QP2010S and my vacuum pump is excessively loud. I'm planning on relocating the pump behind the wall but, due to existing equipment in that room, the vacuum hose is short by about 8 inches. I'm told that Shimadzu's engineers "determined the optimal length" of the hose and that no other lengths are sold/recommended. I've found that Agilent supplies hose of a specific length, as well, but could not determine if alternate lengths were sold.

Not being one of the instrument manufacturers engineers, I'm not privy to whatever information they have regarding hose length, but I'm having a hard time determining why length is so important. I realize it's a volume-related thing but my rough pump, by itself, gets me to the vacuum level needed to run MS. With the turbo pump initiated, I have absolutely no issues and am well in the green at 1.8 Pa. I can't see a small increase in volume would have a dramatic change on anything.

If I ordered hose long enough to do what I want (another foot), what harm would befall my system? Please, let me know your thoughts on this.

[JMB]

Although vacuum theory requires short, wide-bore tubing for optimum pumping capacity, I have used several Finnigan/Thermo & VG MS systems where the roughing pumps were located well away to the rear; and this was variously thermospray or ESI at 1 mL/min.

Never a pump-down or vacuum issue !!

[IdiotFool]

Although vacuum theory requires short, wide-bore tubing for optimum pumping capacity, I have used several Finnigan/Thermo & VG MS systems where the roughing pumps were located well away to the rear; and this was variously thermospray or ESI at 1 mL/min.

Never a pump-down or vacuum issue !!

Thanks for the real-world experience. I'm trying to convince Shimadzu to sell me an extra foot, as that's all I really need to put it behind a wall. There is much warning and cries of doom, but I just don't buy it. We'll see how it goes.

[01310040231]

Two considerations:

1. The pump capacity. If you have a very small pump, it may not work well for you.

2. If your system has any warranty, you want to make sure you follow the instrucations from Shimadzu; otherwise, if you have a problem they may make you to pay for it.

[lmh]

It's not just volume, it's also length. You have a vacuum gradient from wherever air is getting into the system to where it is taken out. The pump will get down to a certain level, and any point between the pump and the pressure will gradually increase from there to the leak. If the pressure-sensitive bits of instrument are somewhere along the path, then changing the hose-length will change the vacuum level where they're operating. Think of it like an electrical circuit with a set of resistors, and you're adding another resistor in series; it changes the voltage at all points along the series of resistances.

This may not matter. If you're communicating with Shimadzu, I'd try to get a face-to-face conversation with an engineer, and ask him/her about the symptoms of things going wrong. They'll never sell you the hose because it's probably pre-cut in the right lengths and sold with a part-number, and they're not going to make a special part-number so they can sell you an extra foot; if you want a hose you'll have to get it from a general hose supplier. But they may advise on what could go wrong, and what symptoms you can expect, and they may agree that if their engineer has a look at the system and declares it to be working within parameters with the extra foot, then they'll continue to support you as a normal customer??

[chemstation]

As lmh mentioned, there is a diameter to length ratio, as the Rough pump needs
work harder to draw the gas in, You didn't mentioned if you were running CI, which
easy has a ~5mls/min extra flow, as opposed to the classical ~1ml/min.

http://www.duniway.com/catalog/su-tubing-clamps.php

http://www.pchemlabs.com/product.asp?pid=1646

and you should be able to join with 1 o-ring and a clamp.