Oil Mist Traps: Eight Models and Selection by Vacuum Pump Capacity

The actual VOMT-250. The transparent case lets you see the filter inside.

At a Glance

Use: capturing oil mist at the exhaust of oil-sealed vacuum pumps

Lineup: VOMT-250, 1000, 1500 and 2000 plus the S series with SS304 cases, eight models in total

Selection criteria: vacuum pump capacity (L/min), exhaust NW size, case and gasket material

Option: safety vent that opens at 2bar or more (VOMT-1500, 2000, S1500, S2000)

Information for inquiries: pump model and capacity, exhaust size, oil type, exhaust gas, installation space

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In an oil-sealed rotary vane vacuum pump (a pump that seals its rotating parts with oil), pump oil leaves through the exhaust as vapor and fine droplets (oil mist) during operation, and the oil level drops. The part that catches this oil mist at the exhaust is the oil mist trap, and the VOMT series divides the pump capacity range of 50~2000L/min into eight models.

If you see oil stains or white smoke around the exhaust, or the oil top-up interval has become shorter, check the trap on the exhaust side first.

This article is based on the VOMT catalog, and VALVEPARK is an online dealer of OMT.

Why Oil Mist Forms in the Exhaust of Oil-Sealed Vacuum Pumps

In an oil-sealed pump, oil closes the gaps around the rotating parts and cools the pump, and because the operating temperature is high, oil vapor comes out of the exhaust together with the gas.

The more gas and vapor the pump draws in, the greater the oil loss, and the loss is even greater when gas ballast is used, which admits air so that condensable vapors do not condense inside the pump. Running without filtering the oil, in the worst case about 2cm³ of oil can be lost for every 1m³ of air at standard conditions that is pumped.

The oil mist separator fitted to the pump as standard does not remove all of the vapor, so some sites require the exhaust to be routed outside the building.

Oil mist filtered at the exhaust

Structure of the Oil Mist Trap

The VOMT is a cylindrical trap connected to the pump exhaust with an NW (KF) flange, and oil droplets are caught as the exhaust passes through the filter material inside the case.

The filter is made of glass fiber and is fastened with a clamp and a single bolt using the One-Bolt method. The filtered oil collects at the bottom of the case.

The cover and clamp of the VOMT-250

The VOMT-250 and VOMT-1000 have transparent cases so you can check the inside by eye, and the VOMT-1500 and VOMT-2000 let you see the oil level at the bottom.

Side view of the VOMT-250. The filter is visible inside the transparent case, and the top is fastened with a clamp.

A concept diagram of how oil droplets in the exhaust are caught on the filter and oil collects below; the port positions and number of droplets differ from the actual product

Three Selection Criteria

Deciding in the order of pump capacity, exhaust size, and case and gasket narrows down the model.

1️⃣ Vacuum pump capacity: the catalog divides models by vacuum pump capacity (L/min), and where capacity ranges meet, the choice is made by looking at the pump model and operating conditions.

2️⃣ Exhaust size: check the NW designation of the pump exhaust; the sizes available differ by model.

3️⃣ Case and gasket: the VOMT-250 and 1000 let you see inside, and the VOMT-1500 and 2000 let you see the oil level at the bottom. The VOMT-250, 1000 and 1500 use silicone gaskets, while the S series uses SS304 cases and EPDM gaskets.

The bottom port of the VOMT-250. The sample in the photo is KF25 size

Pressure at the pump exhaust rises by the amount it takes to pass through the exhaust filter, and as oil builds up on the filter, exhaust resistance can increase further. Check that the exhaust piping follows a route where condensate does not run back into the pump.

For pumps exhausting corrosive gases, choose the model after checking the gas type and concentration. The trap is a part that filters oil droplets, and the exhaust treatment of hazardous gases follows the site's safety standards.

VOMT Series Lineup and VALVEPARK Recommended Configurations

By pump capacity range, the models are divided into standard models and the S series with SS304 cases, and the specifications in the table are catalog values.

VOMT-250 and S250, 1000 and S1000, 1500 and S1500, 2000 and S2000 (catalog photo)

By capacity range, they are as follows.

50~500L/min: VOMT-250, VOMT-S250

50~1000L/min: VOMT-1000, VOMT-S1000

1000~1500L/min: VOMT-1500, VOMT-S1500

1500~2000L/min: VOMT-2000, VOMT-S2000

The configurations divided by pump capacity range and case material are as follows.

VALVEPARK Recommended Configurations

Frequently Asked Questions

Q. My pump exhaust is NW-25. Can I connect it to the larger models?

The VOMT-1500 and VOMT-2000 let you choose NW-25 for the bottom flange, so they can be connected to NW-25 piping. The main flange is NW-40, so also check the size of the piping that connects to the pump exhaust.

Q. Won't the pump exhaust pressure rise if the trap clogs?

It can, because exhaust resistance can increase as oil builds up on the filter. According to the catalog, the VOMT-1500, 2000, S1500 and S2000 can be fitted with an optional safety vent that opens automatically when a pressure of 2bar or more develops. Check the exhaust pressure your pump allows in the pump documentation, and since the filter replacement interval depends on the amount of oil and the gas load, set it by inspecting during operation.

Q. Can the S series be used on pumps that exhaust corrosive gases?

It can only be judged after checking the gas type and concentration. The S series uses SS304 cases and EPDM gaskets, but it does not suit every gas. Please let us know the process gas and the type of pump oil.

Information to Prepare for a Quote Inquiry

If you send us the information below, we can start reviewing the right model.

1️⃣ Vacuum pump model and capacity (L/min)

2️⃣ Exhaust size (NW designation) and the size of the connecting piping

3️⃣ Type of pump oil and the gases mixed in the exhaust

4️⃣ Operating pressure range

5️⃣ Installation space (width and height) and quantity

If you need a specification sheet or detailed documents, please contact us.

▸ View product: OMT VOMT oil mist trap models

OMT oil mist trap modelsVALVEPARK is an online dealer of OMT products.www.valvepark.com

▸ See also: Vacuum KF hinged clamp (aluminum, double pin)

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