Remeza LB50/LB75 Lower Valve Block Gasket (R31481, part no. 21151005)

1. Purpose and operating principle

The gasket separates the cylinder chamber from the valve plate and stops compressed air and oil from escaping through the joint. Output and delivery pressure depend on its condition: a crushed gasket, or one that has lost its resilience, leads to loss of compression and overheating of the block head.

In the Remeza parts diagram the part is item no. 31. The upper and lower valve block gaskets are different parts, so the lower one must be ordered specifically, by code.

2. Technical specifications

Data source: product page of the official Remeza dealer (remeza24.ru).

⚠️ Not confirmed by the manufacturer in public sources: gasket material, maximum operating temperature and pressure, exact outline shape and hole positions, weight, tightening torque for the valve plate fasteners. Please check with an Acvatron manager or the block’s manual. The 100×100 mm dimensions are as stated by the dealer — compare them with the old gasket before replacing.

3. Design features

Design points:

• thin flat part, located between the cylinder block and the valve plate;
• works as a static joint seal — no moving parts;
• consumable element: must be replaced every time the valve assembly is opened;
• one part fits both LB-50 and LB-75 blocks.

4. Installation recommendations

• Replace the gasket at every overhaul of the valve group — a removed gasket must not be reused: it is already crushed along its outline.
• Before installing, clean the mating surfaces of the cylinder block and valve plate of old gasket residue, carbon and oil; do not scratch the surfaces.
• Make sure you are fitting the lower gasket (item no. 31), not the upper one: check against the parts diagram and the shape of the removed part.
• Align the gasket holes with the holes in the block and plate — a blocked air passage or valve port reduces output.
• Tighten the plate fasteners in a criss-cross pattern, in several passes, to the torque given in your block’s manual (⚠️ we do not state a value here — the manufacturer does not provide it on the part page).
• Do not apply sealant to the gasket unless your block’s manual requires it.
• After assembly, run a test start and check the joint for oil and air leaks.

5. Alternatives and comparison

Cross-references. No verified alternative part numbers for R31481 / 21151005 were found in public sources, so we do not list generic “equivalents”. If you need a non-original replacement, send the old gasket or its dimensions to an Acvatron manager — we will match it by size and fit.

Neighbouring items:

6. Common mistakes

• Upper gasket fitted instead of the lower one. The names are similar, the codes differ — order by R31481 / 21151005 and item no. 31.
• Old gasket reused after opening the valve assembly — the loss of compression returns soon after.
• Gasket chosen “by the name LB50/LB75”. There are different valve plate gaskets on the market (including round Ø80 mm ones) — those are other parts.
• Mating surfaces not cleaned. Old gasket residue and carbon cause poor clamping and oil seepage.
• Plate tightened in one pass and in a circle. Plate distortion blows the gasket at the edge.
• Only the gasket replaced, valve plates not checked. If the loss of output comes from worn valve plates, a new gasket will not fix it.

7. Applications

Maintenance and repair of Remeza LB-50 and LB-75 oil-lubricated piston blocks (in Remeza/Aircast compressors fitted with these blocks): replacement when the valve assembly is opened, curing loss of output and head overheating, scheduled block overhaul.

8. Expert opinion

“The lower gasket is the cheapest part of the valve assembly, but whether the block holds pressure depends directly on it. If you have opened the valve plate, change the gasket right away — do not try to reassemble on the old one: saving a few dozen lei is later paid for with compressor downtime. And make sure it is exactly the lower gasket from your own parts diagram.”

— Vitali Boluchevski, Lead Engineer, Acvatron SRL, 18 years of experience

9. FAQ

How does the lower valve block gasket differ from the upper one? They are two different valve block parts: the lower one sits between the cylinder block and the valve plate (item no. 31 in the parts diagram), the upper one on the opposite side of the plate. They are not interchangeable — order by code.

Which blocks does R31481 fit? According to the official Remeza dealer, the gasket is used on LB-50 and LB-75 piston blocks.

What are the dimensions of the R31481 lower gasket? According to the dealer: 100 × 100 mm, height (thickness) 5 mm. Compare with the old part before replacing.

Can the valve block gasket be reused? No. The gasket is a consumable: a new one is fitted at every overhaul of the valve group.

How can I tell the gasket is crushed or blown? Typical signs: lower output and delivery pressure, head overheating, oil seepage or traces of escaping air at the joint between the valve plate and the block. An exact diagnosis is made after opening and inspecting the valve assembly.